#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fastio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

int32_t main()
{
    fastio
    
    int m, p , s, d;
    cin >> p >> d >> m >> s;
    int cnt = 0;
    int prevp = p;
    while( s >= prevp)
    {
        //cout<<prevp<<"\n";
        s -= prevp;
        prevp -= d;
        prevp = max(prevp,m);
        cnt++;
    }
    cout<<cnt;
    return 0;
}