#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
    if(s<p)
        return 0;
    if(s==p)
        return 1;
    int ct=1;
    int amt=s-p;
    int cost=p-d;
    while(cost > m&&amt >0){
        ct++;
        amt-=cost;
        cost-=d;
    }
    ct+=amt/m;
    return ct;
}

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;
}