n, m = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
pos = 0
for i in a:
	pos += (pos < len(b) and b[pos] >= i)
print(pos)

#include <bits/stdc++.h>

using namespace std;

int main() {
#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
//	freopen("output.txt", "w", stdout);
#endif
	
	string s;
	cin >> s;
	
	string ans;
	
	int cnt = 0;
	for (auto c : s) {
		if (c == '1') ++cnt;
		else ans += c;
	}
	
	int n = ans.size();
	int pos = -1;
	while (pos + 1 < n && ans[pos + 1] == '0') ++pos;
	ans.insert(pos + 1, string(cnt, '1'));
	
	cout << ans << endl;
	
	return 0;
}

#include <bits/stdc++.h>

#define forn(i, n) for (int i = 0; i < int(n); i++)

using namespace std;

typedef long long li;

int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	
	li neg = ((n - 1) / 2) * li((n - 1) / 2 + 1);
	if (n % 2 == 0) neg += n / 2;
	li pos = n * li(n - 1) / 2;
	
	li ans = 0;
	forn(i, m){
		int x, d;
		scanf("%d%d", &x, &d);
		ans += x * li(n);
		if (d < 0)
			ans += neg * d;
		else
			ans += pos * d;
	}
	
	printf("%.15f\n", double(ans) / n);
	return 0;
}

#include <bits/stdc++.h>

#define forn(i, n) for (int i = 0; i < int(n); i++)

using namespace std;

const int N = 100000;

pair<int, int> ans[N];

int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	
	if (m < n - 1) {
		puts("Impossible");
		return 0;
	}
	
	int cur = 0;
	
	forn(i, n) for (int j = i + 1; j < n; ++j){
		if (cur == m)
			break;
		if (__gcd(i + 1, j + 1) == 1)
			ans[cur++] = make_pair(j, i);
	}
	
	if (cur != m){
		puts("Impossible");
		return 0;
	}
	
	puts("Possible");
	forn(i, m)
		printf("%d %d\n", ans[i].first + 1, ans[i].second + 1);
	
	return 0;
}

#include<bits/stdc++.h>

using namespace std;

const int MOD = 998244353;

int add(int x, int y)
{
    x += y;
    while(x >= MOD)
        x -= MOD;
    while(x < 0)
        x += MOD;
    return x;
}

int mul(int x, int y)
{
    return (x * 1ll * y) % MOD;
}

int main()
{
    int n;
    scanf("%d", &n);
    vector<int> a(n);
    for(int i = 0; i < n; i++)
        scanf("%d", &a[i]);
        
    int ans = 0;
    vector<int> pw2(1, 1);
    while(pw2.size() < n)
        pw2.push_back(mul(pw2.back(), 2));
    int cur = mul(pw2[n - 1], a[0]);
    for(int i = 0; i < n; i++)
    {
        ans = add(ans, cur);
        if(i < n - 1)
        {
            cur = add(cur, -mul(pw2[n - 2 - i], a[i]));
            cur = add(cur, mul(pw2[n - 2 - i], a[i + 1]));
        }
    }
    printf("%d\n", ans);
}

#define _CRT_SECURE_NO_WARNINGS

#include <vector>
#include <cstdio>
#include <iostream>
#include <algorithm>

// RJ? No, thanks

using namespace std;

const int N = 1000043;

struct state
{
	vector<int>* a;
	int cur_max;
	int sz()
	{
		return a->size();
	}
	void add(int i, int val)
	{
		(*a)[i] += val;
		if(make_pair((*a)[i], i) > make_pair((*a)[cur_max], cur_max))
			cur_max = i;
	}
};

state pull(state z)
{
	if(z.sz() == 0)
	{
		state c;
		c.a = new vector<int>(1, 1);
		c.cur_max = 0;
		return c;
	}
	else
	{
		state c;
		c.a = z.a;
		c.cur_max = z.cur_max;
		c.a->push_back(0);
		c.add(c.sz() - 1, 1);
		return c;
	}
}

state merge(state a, state b)
{
	if(a.sz() < b.sz())
		swap(a, b);
	state c;
	c.a = a.a;
	c.cur_max = a.cur_max;
	int as = c.sz();
	int bs = b.sz();
	for(int i = 0; i < bs; i++)
		a.add(as - i - 1, (*(b.a))[bs - i - 1]);
	return a;
}

state s[N];
int ans[N];
vector<int> g[N];

void dfs(int x, int p = -1)
{
	s[x].a = new vector<int>(0);
	s[x].cur_max = 0;
	for(auto y : g[x])
		if(y != p)
		{
			dfs(y, x);
			s[x] = merge(s[x], s[y]);
		}
	s[x] = pull(s[x]);
	ans[x] = s[x].sz() - s[x].cur_max - 1;
}

int main()
{
	int n;
	scanf("%d", &n);
	for(int i = 0; i < n - 1; i++)
	{
		int x, y;
		scanf("%d %d", &x, &y);
		--x;
		--y;
		g[x].push_back(y);
		g[y].push_back(x);
	}
	dfs(0);
	for(int i = 0; i < n; i++)
		printf("%d\n", ans[i]);
	return 0;
}

#include<bits/stdc++.h>

using namespace std;

#define sz(a) ((int)(a).size())

struct edge
{
    int y;
    int c;
    int f;
    edge() {};
    edge(int y, int c, int f) : y(y), c(c), f(f) {};
};

const int N = 100;

vector<edge> e;
vector<int> g[N];
int edge_num[N][N];
int char_vertex[6];
int mask_vertex[N];
int used[N];
int cc = 0;
int s, t;

void add_edge(int x, int y, int c)
{
    edge_num[x][y] = sz(e);
    g[x].push_back(sz(e));
    e.push_back(edge(y, c, 0));
    edge_num[y][x] = sz(e);
    g[y].push_back(sz(e));
    e.push_back(edge(x, 0, 0));
}

int rem(int num)
{
    return e[num].c - e[num].f;
}

int dfs(int x, int mx)
{
    if(x == t) return mx;
    if(used[x] == cc) return 0;
    used[x] = cc;
    for(auto num : g[x])
    {
        if(rem(num))
        {
            int pushed = dfs(e[num].y, min(mx, rem(num)));
            if(pushed)
            {
                e[num].f += pushed;
                e[num ^ 1].f -= pushed;
                return pushed;
            }
        }
    }
    return 0;
}

bool check(int ch, int mask)
{
    if((mask & (1 << ch)) == 0)
        return false;
    int cv = char_vertex[ch];
    int mv = mask_vertex[mask];
    int e1 = edge_num[s][cv];
    int e2 = edge_num[mv][t];
    if(e[e1].f == 0 || e[e2].f == 0)
        return false;
    e[e1].f--;
    e[e1 ^ 1].f++;
    vector<int> affected_edges;
    affected_edges.push_back(e1);
    for(auto x : g[cv])
    {
        if((x & 1) == 0 && e[x].f > 0)
        {
            affected_edges.push_back(x);
            e[x].f--;
            e[x ^ 1].f++;
            int y = e[x].y;
            for(auto x2 : g[y])
            {
                if((x2 & 1) == 0)
                {
                    affected_edges.push_back(x2);
                    e[x2].f--;
                    e[x2 ^ 1].f++;
                    break;
                }
            }
            break;
        }
    }
    if(e[e2].f < e[e2].c)
    {
        e[e1].c--;
        e[e2].c--;
        return true;
    }
    affected_edges.push_back(e2);
    e[e2].f--;
    e[e2 ^ 1].f++;
    for(auto x : g[mv])
    {
        if((x & 1) == 1 && e[x].f < 0)
        {
            affected_edges.push_back(x ^ 1);
            e[x].f++;
            e[x ^ 1].f--;
            int y = e[x].y;
            for(auto x2 : g[y])
            {
                if((x2 & 1) == 1)
                {
                    affected_edges.push_back(x2 ^ 1);
                    e[x2].f++;
                    e[x2 ^ 1].f--;
                    break;
                }
            }
            break;
        }
    }
    cc++;
    e[e1].c--;
    e[e2].c--;
    if(dfs(s, 1))
        return true;
    else
    {
        e[e1].c++;
        e[e2].c++;
        for(auto x : affected_edges)
        {
            e[x].f++;
            e[x ^ 1].f--;
        }
        return false;
    }
}

char buf[100043];
string allowed[100043];
int allowed_mask[100043];

int main()
{
    s = 70;
    t = 71;
    scanf("%s", buf);
    string z = buf;
    int n = sz(z);
    int m;
    scanf("%d", &m);
    for(int i = 0; i < n; i++)
    {
        allowed[i] = "abcdef";
        allowed_mask[i] = 63;
    }
    for(int i = 0; i < m; i++)
    {
        int idx;
        scanf("%d", &idx);
        --idx;
        scanf("%s", buf);
        allowed[idx] = buf;
        allowed_mask[idx] = 0;
        for(auto x : allowed[idx])
        {
            allowed_mask[idx] |= (1 << (x - 'a'));
        }
    }
    for(int i = 0; i < 6; i++)
        char_vertex[i] = i;
    for(int i = 0; i < (1 << 6); i++)
        mask_vertex[i] = i + 6;
    for(int i = 0; i < (1 << 6); i++)
        for(int j = 0; j < 6; j++)
            if(i & (1 << j))
                add_edge(char_vertex[j], mask_vertex[i], 100000);
    for(int i = 0; i < 6; i++)
    {
        int cnt = 0;
        for(int j = 0; j < n; j++)
            if(z[j] == 'a' + i)
                cnt++;
        add_edge(s, char_vertex[i], cnt);
    }
    for(int i = 0; i < (1 << 6); i++)
    {
        int cnt = 0;
        for(int j = 0; j < n; j++)
            if(allowed_mask[j] == i)
                cnt++;
        add_edge(mask_vertex[i], t, cnt);
    }
    int flow = 0;
    while(true)
    {
        cc++;
        int p = dfs(s, 100000);
        if(p)
            flow += p;
        else
            break;
    }
    if(flow != n)
    {
        puts("Impossible");
        return 0;
    }
    for(int i = 0; i < n; i++)
        for(int j = 0; j < 6; j++)
        {
            if(check(j, allowed_mask[i]))
            {
                printf("%c", j + 'a');
                break;
            }
        }
    puts("");
}