#include <bits/stdc++.h>

using namespace std;
void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int main() {
    fast_io();
    int b0, c0, b1, c1;
    cin >> b0 >> c0 >> b1 >> c1;
    c0 = (c0 % b0 + b0) % b0;
    c1 = (c1 % b1 + b1) % b1;
    for (int i = 0; i < b0 * b1; i++) {
        if (i % b0 == c0 && i % b1 == c1) {
            cout << i << endl;
            return 0;
        }
    }
    cout << "NaN" << endl;
}