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

template <typename T>
T inv(T a, T m) {
	T u = 0, v = 1;
	T old = m;
	while (a != 0) {
		T t = m / a;
		m -= t * a; swap(a, m);
		u -= t * v; swap(u, v);
	}
	assert(m == 1);
	if(u < 0){
		u += old;
	}
	return u;
}
// x == a[i] mod m[i]
int crt(vector<int> a,vector<int> m){
	int n = a.size();
	int prod = 1;
	vector<int> M(n);
	vector<int> y(n);
	for(int i = 0; i < n; i++){
		prod *= m[i];
	}
	for(int i = 0; i < n; i++){
		M[i] = prod / m[i];
		if(__gcd(M[i],m[i]) != 1){
			return -1;
		}
		y[i] = inv(M[i],m[i]);
	}
	int x = 0;
	for(int i = 0; i < n; i++){
		(x += a[i] * y[i] * M[i]) %= prod;
	}
	return x;
}

int main(){
	ios::sync_with_stdio(false);cin.tie(0);
	vector<int> a(2),m(2);
	for(int i = 0; i < 2; i++){
		cin >> m[i] >> a[i];
		if(a[i] < 0){
			a[i] += m[i];
		}
	}
	int ans = crt(a,m);
	if(ans == -1){
		cout << "NaN";
	}
	else{
		cout << ans;
	}
	return 0;
}