#include <bits/stdc++.h>
using namespace std;

int main()
{
    int A, B, a, b;
    cin >> A >> B >> a >> b;
    int ans = a;
    int i = 0;
    while (true)
    {
        ans = A * i + a;
        if (ans % B == b)
            break;
        i++;
    }
    cout << ans << endl;
}