#include <iostream>
using namespace std;

int main()
{
    int b[2], c[2];
    cin >> b[0] >> c[0] >> b[1] >> c[1];
    while (c[0] < 0)
    {
        c[0] += b[0];
    }
    while (c[1] < 0)
    {
        c[1] += b[1];
    }
    for (int i = 0; i <= 10000; i++)
    {
        if (i % b[0] == c[0] % b[0] && i % b[1] == c[1] % b[1])
        {
            cout << i << endl;
            return 0;
        }
    }
    cout << "NaN" << endl;
}