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

int inv(int a, int m)
{
    int m0 = m, t, q;
    int x0 = 0, x1 = 1;
    if (m == 1)
        return 0;
    while (a > 1) {
        q = a / m;
        t = m;
        m = a % m, a = t;
        t = x0;
        x0 = x1 - q * x0;
        x1 = t;
    }
    if (x1 < 0)
        x1 += m0;
    return x1;
}

int main() {
    int b0, c0, b1, c1;
    scanf("%d %d %d %d", &b0, &c0, &b1, &c1);
    while (c0 < 0)
        c0 += b0;
    while (c1 < 0)
        c1 += b1;
    if (abs(c1 - c0) % __gcd(b1, b0) != 0)
        cout << "NaN";
    else {
        int res = (c0 * b1 * inv(b1, b0) + c1 * b0 * inv(b0, b1)) % (b0 * b1);
        cout << res;
    }
    return 0;
}