#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
   int A,B,a,b;
   cin >> A >> B >> a >> b;
   rep(i,10000000) if(i%A==a && i%B==b){
    cout << i << endl;
    break;
   }
}