using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    internal static void Main() => new Program().Solve();

    void Solve()
    {
        //code
        var h = IO.Read<int>();
        var w = IO.Read<int>();
        int ans;

        if (h % 2 == 0)
        {
            if (w % 2 == 0)
            {
                ans = h * w;
                IO.Write(ans);
            }
            else
            {
                ans = h * (w - 1);
                IO.Write(ans);
            }
        }
        else
        {
            if (w % 2 == 0)
            {
                ans = (h - 1) * w;
                IO.Write(ans);
            }
            else
            {
                ans = (h - 1) * (w - 1) + 2;
                IO.Write(ans);
            }
        }

        #region A
        //int n = IO.Read<int>();
        //var linklist = new LinkedList<int>();
        //for (int i = 1; i <= n; i++)
        //{
        //    linklist.AddLast(i);
        //}
        //for (int i = 0; i < n; i++)
        //{
        //    IO.WriteEnum<int>(linklist);
        //    LinkedListNode<int> node = linklist.First;
        //    linklist.RemoveFirst();
        //    linklist.AddLast(node);
        //}
        #endregion
    }

}

static class IO
{
    static readonly Queue<string> que = new Queue<string>();
    public static T Read<T>() { if (!que.Any()) foreach (var s in Console.ReadLine().Split()) que.Enqueue(s); return (T)Convert.ChangeType(que.Dequeue(), typeof(T)); }
    public static IEnumerable<T> ReadEnum<T>(long n) { for (long i = 0; i < n; i++) yield return Read<T>(); }
    public static void Write<T>(T item) => Console.WriteLine(item);
    public static void WriteEnum<T>(IEnumerable<T> items, string separetor = " ") => Write(string.Join(separetor, items));
}