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

int main(){
    int A, B, a, b;
    cin >> A >> B >> a >> b;
    for (int i = 0; i <= A * B; i++) {
        if (i % A == a and i % B == b) {
            cout << i << endl;
            return 0;
        }
    }
    
    return 0;
}