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

namespace mytest_13_
{
    class Program
    {
        public static int  Rom(int n, int m)//雙寄或雙偶
        {
            int count = 0;//第一排Y坐標上要幾個         
            if (n < m)
            {
                for (int i = 1; i <= n; i = i + 2)
                {
                    count++;
                }

            }
            else
            {
                for (int j = 1; j <= m; j = j + 2)
                {
                    count++;
                }

            }
          

            return count;
        
        }
        public static int Fjando(int n,int m)//一奇數一偶數
        {
            int count = 0;
            for (int j = 0; j < n; j = j + 2)
            {
                count++;
            }
            int tmp = m / 2 + 1;
            //int tmp2 = n / 2;
            count = count * tmp;
            return count;
            
        }
        public static int  Cal(int n,int m)
        {
            int count=0;
            int x=0;
            int y=0;
            if (n <= m)
            {
                y = n;
                x = m;
            }
            else
            {
                y = m;
                x = n;
            }
            if ((n % 2 == 0) && (m % 2 == 0))
            {
                count = Rom(n, m);
                count = count * x / 2 + y / 2;
            }
            if ((n % 2 != 0) && (m % 2 != 0))
            {
                count = Rom(n, m);
                int tmp = 2 * count - 1;
                int tmp2 = x / 2 + 1;
                count = tmp * tmp2;

            }
            if (((n % 2 == 0) && (m % 2 != 0)) || (((n % 2 != 0) && (m % 2 == 0))))
            {
                if (n % 2 == 0)
                {
                    count = Fjando(n, m);

                }
                if (m % 2 == 0)
                {
                    count = Fjando(n, m);
                }
               
            }
            return count;
        
        }
        static void Main(string[] args)
        {
            int num = Cal(6,4);
            Console.WriteLine(num);
        }
    }
}