#include<bits/stdc++.h>
using namespace std;
#define int long long

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