#include <bits/stdc++.h>
using namespace std;
int main() {
    int p, d, m, s, cnt, curcost;
    scanf ("%d %d %d %d", &p, &d, &m, &s);
    cnt = 0;
    curcost = p;
    while (curcost<=s)
    {
        s-=curcost;
        cnt++;
        curcost = max(curcost-d, m);
    }
    printf ("%d", cnt);
    return 0;
}