#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 sum=0,i=-1;
    while(s>=sum)
    { sum+=p;
     if(p!=m)
     p=p-d;
    if(p<=m)
     p=m;
        
     i++;
    }  
    return i;
}

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