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


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