//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#include <atcoder/modint>
#include <atcoder/dsu>
#include <boost/rational.hpp>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
const double pi = 3.14159265359879323846264338327950288419;
const ll INF = 9 * 1e18;
using p = pair<ll, ll>;

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