#include <bits/stdc++.h>
#include <atcoder/all>
using ll = long long;
#define MOD 1000000007
#define Mod 998244353
const int MAX = 1000000005;
const long long INF = 1000000000000000005LL;
using namespace std;
using namespace atcoder;



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