#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    int n=((m-p)/d)+1;
    int sn=0;
    for(int i=-1;i<n-1;++i)
    {
        sn=sn+(p+(i+1)*d);
    }
    int c1=0,c2;
    if(sn>=s)
    {
        int r=s;
        int i=-1;
        while(r>=p+(i+1)*d)
        {
            c1++;
            r=r-(p+(i+1)*d);
            i++;
        }
        return c1-4;
    }
    else if(sn<s)
    {
        int r=s-sn;
        int c2=n+r/m;
        return c2-4;
    }
    return 0;
}

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;
}