#include <bits/stdc++.h>
//#include<atcoder/all>
using namespace std;
//using namespace atcoder;
using ll = long long;
const ll mod = 1000000007;
//const ll mod = 998244353;
int A, B, a, b;
int main() {
	cin >> A >> B >> a >> b;
	int  now = 0;
	while (1) {
		if (((A * now+a) % B) == b) {
			cout << A * now + a << endl;
			return 0;
		}
		now++;
	}
}