#include <bits/stdc++.h>
#if __has_include("./debug.cpp")
#include "./debug.cpp"
#else
#define debug(...)
#define print_line
#endif
using namespace std;
using ll = long long;

int main() {
	int A, B, a, b;
	cin >> A >> B >> a >> b;
	for (int i = 0; i <= 9000000; i++) {
		if (i % A == a && i % B == b) {
			cout << i << endl;
			;
			return 0;
		}
	}
}