#include <iostream>

using namespace std;

int main()
{
    long long int cn1, cn2, x, y;
    cin >> cn1 >> cn2 >> x >> y;
    long long a = (x*y*(cn1+cn2-1))/(x*y-1);
    long long ans = a+1;
    if (ans/y - ans/(x*y) > cn1)
    {
        ans = ((cn2-1)*y)/(y-1)+1;
    }
    else if (ans/x - ans/(x*y) > cn2)
    {
        ans = ((cn1-1)*x)/(x-1)+1;
    }
    cout << ans;
    return 0;
}