#include<bits/stdc++.h>
using namespace std;

int main() {
	unsigned int a, b, c, d;
	cin >> a >> b >> c >> d;
	if (a * 1.0 / c == b * 1.0 / d) {

		cout << a / c;
	} else if (a == 0 && c == 0) {
		cout << b / d;
	} else if (b == 0 && d == 0) {
		cout << a / c;
	} else {
		cout << -1;
	}
}