#include <bits/stdc++.h>

using namespace std;



int main() {
    int p,i,j,t=0,o=0,u;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    while(p>=m)
    {   if(s<=0){cout<<o-1;break;}
        s-=p;
        p-=d;
     o++;
    }
    if(s>=0)
    {
        u=s/m;
        cout<<u+o;
        return 0;
    }


    return 0;
}