#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;
template <class T = ll>
using vc = vector<T>;
template <class T = ll>
using vvc = vc<vc<T>>;
void solve();
int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    ll t = 1;
    // cin >> t;
    for (int i = 1; i <= t; i++) solve();
    return 0;
}

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