#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
#include <map>
#include <queue>
using namespace std;

int main(){
    int b0,c0,b1,c1;
    cin >> b0 >> c0 >> b1 >> c1;
    if(c0<0) c0 += b0;
    if(c1<0) c1 += b1;
    c0 %= b0;
    c1 %= b1;

    for(int i = 0;i<b0*b1;i++){
        if(i%b0==c0%b0){
            if(i%b1==c1%b1){
                cout << i << endl;
                return 0;
            }
        }
    }

    cout << "NaN" << endl;
}