#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) { return (ull)rng() % B; }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int A, B, a, b;
    cin >> A >> B >> a >> b;
    for (int i = 0;; i++) {
        if (i % A == a and i % B == b) {
            cout << i << endl;
            break;
        }
    }
}