#include<bits/stdc++.h>
using namespace std;
vector<int> g[200001];
long maxSum(int n, vector<vector<int>> edges){
    for(auto j:edges){
        g[j[0]].push_back(j[1]);
        g[j[1]].push_back(j[0]);
    }
    queue<int> q;
    vector<bool> vis(n+1);
    vector<int> d(n+1);
    q.push(1);
    vis[1] = true;
    while (!q.empty()) {
        int v = q.front();
        q.pop();
        for (int u : g[v]) {
            if (!vis[u]) {
                vis[u] = true;
                q.push(u);
                d[u] = d[v] + 1;
            }
        }
    }
    int curmin = 1e9;
    long sum = 0;
    for(int i=n; i>=1; i--){
        if(d[i]>curmin) d[i] = curmin;
        curmin = min(curmin, d[i]);
        sum += d[i];
    }
    return sum;
}

int main(){
    int n,m;
    cin >> n >> m;
    vector<vector<int>> edges;
    for(int i=0; i<m; i++){
        int u,v;
        cin >> u >> v;
        edges.push_back({u,v});
    }
    long ans = maxSum(n,edges);
    cout << ans << endl;
}

#include <bits/stdc++.h>
using namespace std;
/* nichijou */
template<class T,class U>
bool cmax(T & a, const U & b) {return a < b ? a = b, 1 : 0;}
template<class T,class U>
bool cmin(T & a, const U & b) {return b < a ? a = b, 1 : 0;}
/* data type */
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define F first
#define S second
/* STL container */
typedef vector<int> vi;
typedef vector<ll> vll;
#define SZ(a) ((int)(a).size())
#define ALL(a) begin(a), end(a)
#define CLR(a) (a).clear()
#define BK(a) ((a).back())
#define FT(a) ((a).front())
#define DB(a) (a).pop_back()
#define DF(a) (a).pop_front()
#define PB push_back
#define EB emplace_back
/* I gave you my heart and then you turned around. */
void _BG(const char * s) {cerr<<s<<endl;}
template<class T, class ... TT>
void _BG(const char * s,T a, TT...b)
{
    for (size_t c = 0; *s && (c || *s != ','); cerr << *s++)
        c += count(ALL("([{"),*s) - count(ALL(")]}"),*s);
    cerr << " = " << a;
    if (*s) {
        cerr << ", ";
        ++s;
    }
    _BG(s,b...);
}
#ifdef PR3PONY
#define BG(...) do { \
    cerr << __PRETTY_FUNCTION__ << ':' << __LINE__ << ": "; \
    _BG(#__VA_ARGS__,__VA_ARGS__); \
} while(0)
#else
#define BG(...)
#endif
/* Good Luck && Have Fun ! */
const int N = 2e5 +87;
vector<int> g[N];
int d[N], p[N], cc;
int find(int x) {return p[x] == x ? x : p[x] = find(p[x]);}
void meld(int a, int b)
{
    a = find(a), b = find(b);
    if (a == b)
        return;
    --cc;
    p[b] = a;
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    for  (int i = 0; i < m; ++i) {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    fill_n(d, n + 1, N);
    d[1] = 0;
    vector<int> q = {1}, nq;
    int mx = 1;
    cc = 1;
    p[1] = 1;
    int ptr = 2;
    for (int k = 0; q.size(); ++k) {
        while (p[ptr])
            ++ptr;
        while (!(ptr == mx + 1 && cc == 1)) {
            d[ptr] = k;
            mx = max(mx, ptr);
            q.push_back(ptr);
            p[ptr] = ptr;
            ++cc;
            for (int v : g[ptr])
                if (p[v]) 
                    meld(v, ptr);
            while (p[ptr])
                ++ptr;
        }

        nq.clear();
        for (int u : q) {
            for (int v : g[u]) {
                if (d[v] != N)
                    continue;
                d[v] = k + 1;
                mx = max(mx, v);
                ++cc, p[v] = v;
                meld(v, u);
                nq.push_back(v);
            }
        }
        swap(q, nq);
    }
    //for (int i = 1; i <= n; ++i) cerr << d[i] << " "; cerr << endl;
    ll ans = 0;
    for  (int i = 1; i <= n; ++i) {
        ans += d[i];
    }
    cout << ans << endl;
}