#include <bits/extc++.h>

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