int main() {
	int a, b, c, d;
	while (cin >> a >> b >> c >> d) {
		int sign = -1;
		for (int i = 0; i < MAX && -1==sign; i++) {
			int t = b + a * i - d;
			if (t%c == 0)sign = i;
		}
		if (sign == -1)cout << -1 << endl;
		else cout << b + a * sign << endl;
	}
}