#include <bits/stdc++.h>

using namespace std;

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