// C++ Program to find sum of Fibonacci numbers in 
// O(Log n) time.
#include <bits/stdc++.h>
using namespace std;
const long long MAX = LLONG_MAX;


// Driver program to test above function

int main()
{
	long long  ans = 0;
	int A,B,a,b;
	cin>>A>>B>>a>>b;
	for(ans=0; ans<MAX; ans++){
		if(ans%A ==a && ans%B == b){
			cout<<ans<<"\n";
			return 0;
		}
	}
}