#include <iostream>
 
using namespace std;
int main() {
    long Hp, Hc, K, M, X;
    cin >> Hp >> Hc >> K >> M;
    if ((M + Hc * K) % Hp != 0) {
    	cout << -1 << endl;
    	return 0;
    }
    X = (M + Hc * K) / Hp;
    if (X < 0) X = -1;
    cout << X << endl;
    return 0;
}