include <bits/stdc++.h>

define fore(i, l, r) for(int i = int(l); i < int(r); i++)

define forn(i, n) fore(i, 0, n)

define all(a) (a).begin(), (a).end()

define sqr(a) ((a) * (a))

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

define mp make_pair

define pb push_back

define x first

define y second

using namespace std;

template<class A, class B> ostream& operator << (ostream &out, const pair<A, B> &p) { return out << "(" << p.first << ", " << p.second << ")"; }

template ostream& operator << (ostream &out, const vector &v) { out << "["; forn(i, sz(v)) { if(i > 0) out << " "; out << v[i]; } return out << "]"; }

typedef long long li; typedef long double ld; typedef pair<int, int> pt;

inline int gett() { return clock() * 1000 / CLOCKS_PER_SEC; }

const ld EPS = 1e-9; const int INF = int(1e9); const li INF64 = li(INF) * INF; const ld PI = 3.1415926535897932384626433832795;

int c, l, v0, v1, a;

inline bool read() { if(!(cin >> c >> v0 >> v1 >> a >> l)) return false;

return true;

}

inline void solve() { int pos = v0; int t = 1;

int add = v0;

while(pos < c) {
    add = min(v1, add + a);

    pos += add - l;
    t++;
}

cout << t << endl;

}

int main(){

ifdef _DEBUG freopen("input.txt", "r", stdin); //freopen("output.txt", "w", stdout);

int t = gett();

endif

srand(time(NULL));
cout << fixed << setprecision(10);

while(read()) {
    solve();   

ifdef _DEBUG cerr << "TIME = " << gett() — t << endl; t = gett();

endif

}
return 0;

}