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

namespace PracticeAtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
			
			
			//ポッキーG
			string sC = Console.ReadLine();
			string[] sD = sC.Split(' ');
			
			int[] after = sD.Select(s => int.Parse(s)).ToArray();
			
			//Array.Sort(after);
			int int2K = after[1] *2; 
			int intL = after[0];
			int cnt = 0;
			
			while(int2K < intL){
				intL = intL - int2K;
				cnt++;
			
			}
				
			Console.WriteLine(cnt* int2K/2);
			
		}
    }
}