#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <set>
#include <map>
using namespace std;

int main() {
  int A, B; cin >> A >> B;
  int a, b; cin >> a >> b;
  for (int i = 0; i < A * B; i++) {
    if (i % A == a and i % B == b) {
      cout << i << endl;
      return 0;
    }
  }
  return 0;
}