#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,ans = 0;
    cin >> p >> d >> m >> s;
    int cost = 0;
    while(cost + p <= s && p >= m) {
        cost += p;
        p = max(p - d, m );
        ++ans;
    }
    cout << ans;
    return 0;
}