using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


   class Program
   {
       static void Main(string[] args)
       {
           string[] line = Console.ReadLine().Split(' ');
         int H = int.Parse(line[0]);
         int W = int.Parse(line[1]);
         if(H / 2 == 0){
         Console.WriteLine(W * (H / 2));
         }else
         {
           Console.WriteLine((W * (H / 2)) + ((W / 2) + 1));
         }
       }
   }
