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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int p,d,m,s;
    int cnt = 0;
    cin >> p >> d >> m >> s;
    while(s>=p){
        cnt++;
        s-=p;
        p-=d;
        if(p < m) p = m;
    }
    cout<<cnt;
    return 0;
}