#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int p,d,m,s,ans=0;
    cin>>p>>d>>m>>s;
    while(s>=0)
    {
        s-=p;
        p-=d;
        if(p<m)
            p=m;
        ans++;
    }
    cout<<ans-1;
    return 0;
}