B. Друзья и подарки

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Numerics;


public static class solver
{
    static long Gcd(long a, long b)
    {
        while (b != 0) {
            var rem = a % b;
            a = b;
            b = rem;
        }
        return a;
    }

    static long cnt1, cnt2, x, y;

    static long CountMatching(long max, long divisor)
    {
        return max / divisor;
    }

    static bool Possible(long max)
    {
        var notFor1 = CountMatching(max, x);
        var notFor2 = CountMatching(max, y);
        var notFor12 = CountMatching(max, x * y);
        var for12 = max - CountMatching(max, Gcd(x, y));

        var left = (max - notFor1) + (max - notFor2) - for12;
        return left >= (cnt1 + cnt2);
    }



    public static void Main()
    {
        var input = Console.ReadLine().Split(null);
        cnt1 = long.Parse(input[0]);
        cnt2 = long.Parse(input[1]);
        x = long.Parse(input[2]);
        y = long.Parse(input[3]);

        var l = 0L;
        var r = long.MaxValue / 2;

        while (l < r - 1) {
            var m = (l + r) / 2;
            if (Possible(m))
                r = m;
            else
                l = m;
        }

        if (Possible(l))
            Console.WriteLine(l);
        else
            Console.WriteLine(r);

#if !ONLINE_JUDGE
        Console.ReadLine();
#endif
    }
}