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

#define rep(i, n) for( ll i = 0; i < n; i++ )
using ll = long long;

int main() {
	ll A, B, a, b;
	cin >> A >> B >> a >> b;
	ll ma = A * B, ans;
	rep(i, ma + 1) {
		if( i % A == a && i % B == b) {
			ans = i;
			break;
		}
	}
	cout << ans << endl;
}