#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001

int main(){
	
	int A,B,a,b;
	cin>>A>>B>>a>>b;
	rep(i,Inf32){
		if(i%A==a&&i%B==b){
			cout<<i<<endl;
			break;
		}
	}
	
	return 0;
}