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

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;
}