#include <bits/extc++.h>

int main() {
    using namespace std;
    long B_0, C_0, B_1, C_1;
    cin >> B_0 >> C_0 >> B_1 >> C_1;
    for(unsigned long i{}; i <= 10000; ++i)if((i - C_0) % B_0 == 0 && (i - C_1) % B_1 == 0){
        cout << i << endl;
        return 0;
    }
    cout << "NaN" << endl;
    return 0;
}