#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#include <queue>
#include <stack>

using namespace std;

typedef long long int ll;
typedef pair<int, int> Pii;

const ll mod = 998244353;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int alpha, beta, a, b;
  cin >> alpha >> beta >> a >> b;

  int ans = 0;
  while (true) {
    if (ans % alpha == a && ans % beta == b) {
      break;
    }
    ans++;
  }

  cout << ans << endl;

  return 0;
}