#include <bits/stdc++.h>
using namespace std;
int main() {
  int A, B, a, b;
  cin >> A >> B >> a >> b;
  int x = 0;
  // cout << "aaa" << endl;
  while (true) {
    if (x % A == a && x % B == b) {
      cout << x << endl;
      break;
    }
    x++;
  }
  // cout << "aaa" << endl;
  return 0;
}