#include <bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, n, m) for (int i = (n); i < (m); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;
using vs = vector<string>;
using pii = pair<int, int>;
using Graph = vector<vector<int>>;

int main() {
  int A, B, a, b; cin >> A >> B >> a >> b;
  FOR(i, 0, 2999*3000){
    if(i%A==a&&i%B==b){
      cout << i << endl;
      return 0;
    }
  }

    
}