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

namespace lecture
{
    class Program
    {

        static void Main(string[] args)
        {
            int[] tmp = Console.ReadLine().Trim().Split(' ').Select(x => int.Parse(x)).ToArray();
            // ポッキーの長さ
            int L = tmp[0];
            // １回でかじる長さ(mm)
            int K = tmp[1];
            int count = 0;
            while (true)
            {   
                if(L <= K*2)
                {
                    break;
                }
                L -= K * 2;
                count++;
            }
            Console.WriteLine(K*count);
        }
    }
}