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