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

int main() {
	int A, B, a, b;
	cin >> A >> B >> a >> b;
	assert(1 <= A && A <= 3000);
	assert(1 <= B && B <= 3000);
	assert(0 <= a && a < A);
	assert(0 <= b && b < B);
	
	int val = 0;
	while (true) {
		if (val % A == a && val % B == b) break;
		val++;
	}
	
	cout << val << endl;
}