#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    int count=0,cost;
    s=s-p;
    cost=p;
    while(s>=m && cost<=s)
    {
        s=s-d;
        cost=cost+d;
        count=count+1;
    }
    return count;
}

int main() {
    int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    int answer = howManyGames(p, d, m, s);
    cout << (answer-1) << endl;
    return 0;
}