#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) std::begin(x), std::end(x)
using namespace std;
using ll = long long;
void opvec1(vector<int> &vec);
void opvec2(vector<vector<int>> &vec);
void opset(set<int> &S);

int main() {
  int c0, c1, b0, b1;
  cin >> b0 >> c0 >> b1 >> c1;
  int n0 = (c0%b0 + b0) % b0;
  int n1 = (c1%b1 + b1) % b1;

  rep(i, b0*b1) {
    
    if (i%b0 == n0 && i%b1 == n1) {
      cout << i << endl;
      return 0;
    }
  }
  cout << "NaN" << endl;
}

//
void opvec1(vector<int> &vec) {
  rep(i, vec.size()) cout << vec[i] << " ";
  cout << endl;
}
void opvec2(vector<vector<int>> &vec) {
  rep(i, vec.size()) {
    rep(j, vec[0].size()) cout << vec[i][j] << " ";
  cout << endl;
  }
}
void opset(set<int> &S) {
  for (auto s: S) cout << s << " ";
  cout << endl;
}