#include <bits/stdc++.h>
using namespace std;
int main(){
	int A, B, a, b;
	cin >> A >> B >> a >> b;
	int x = 0;
	while (true){
		if (x % A == a and x % B == b){
			cout << x << endl;
			return 0;
		}
		x++;
	}
}