#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 cur = p, r = 0;
    
    while (s >= cur) {
        s -= cur; r++;
        cur = max(cur - d, m);
    }
    cout<<r<<endl;
    return 0;
}