#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

int main() {
  int a,b,c,d;cin>>a>>b>>c>>d;
  for (int i = 0; i < 1e7; i++) {
    if(i % a == c && i % b ==d ) {
      cout << i << endl;
      return 0;
    }
  }
  return 0;
}