#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  int a,b,c,d;
  cin>>a>>b>>c>>d;
  swap(a,b);swap(c,d);
  while(a < 0) a += b;
  while(c <  0) c += d;
  a %= b;
  c %= d;
  int n = 0;
  while((n%b != a || n%d != c) && n < 1e7)n++;
  if(n > 1e6){
      cout<<"NaN"<<endl;
      return 0;
  }
  cout<<n<<endl;
}