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