#include <bits/stdc++.h>
using namespace std;
long long a, b;
long long c, d;
int main() {
  while (cin >> a >> b) {
    cin >> c >> d;
    for (int i = 0; i <= 1000; ++i) {
      for (int j = 0; j <= 1000; ++j) {
        if ((b + a * i) == (d + c * j)) {
          cout << b + a * i << endl;
          return 0;
        }
      }
    }
    cout << "-1" << endl;
  }
}
