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

#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...)
#endif

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    int A, B, a, b;
    cin >> A >> B >> a >> b;
    for (int x = 0; x <= A * B; x++) {
        if (x % A == a && x % B == b) {
            cout << x << '\n';
            return 0;
        }
    }
}