#include <bits/stdc++.h>
using namespace std;
#define rep(i, s, n) for (int i = (s); i < (int)(n); i++)
#include <atcoder/all>
using namespace atcoder;
using mint1 = modint1000000007;
using mint2 = modint998244353;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
ld pi=3.141592653589793;
const int inf=2e9;
const ll linf=2e18;
const ld eps=1e-14;
#define Yes cout << "Yes" << endl
#define No cout << "No" << endl

int main() {
    int A,B,a,b;
    cin >> A >> B >> a >> b;
    for(int i=0; i<1e7; i++) {
        if(i%A==a && i%B==b) {
            cout << i << endl;
            return 0;
        }
    }
}