// 

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

using ll = long long;

#define rep(i, n) for (int i=0; i<(int)(n); ++(i))
#define rep3(i, m, n) for (int i=(m); (i)<(int)(n); ++(i))
#define repr(i, n) for (int i=(int)(n)-1; (i)>=0; --(i))
#define rep3r(i, m, n) for (int i=(int)(n)-1; (i)>=(int)(m); --(i))
#define all(x) (x).begin(), (x).end()

const int INF = (int)(1e9);

int main() {
	int a, b, ai, bi;
	cin >> a >> b >> ai >> bi;
	if (a > b) {
		swap(a, b);
		swap(ai, bi);
	}
	int x = bi;
	while (x%a != ai) x += b;
	cout << x << endl;
	return 0;
}