#include<bits/stdc++.h>
using namespace std;
using ll=long long;

int main(){
  ll A,B,a,b;
  cin>>A>>B>>a>>b;
  for(ll x=0;x<=10000000;x++){
    if(x%A==a&&x%B==b){
      cout<<x<<endl;
      exit(0);
    }
  }
}