using System;
using System.Linq;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var line1 = Console.ReadLine().Split(' ').Select(c => int.Parse(c)).ToArray();

            var l = line1[0];
            var k = line1[1];

            int left = l;
            int i = 0;
            for (; ; i++)
            {
                left = left - 2 * k;
                if (left <= 0)
                {
                    break;
                }
            }

            int result = i * k;

            //結果を表示
            Console.WriteLine(result);
        }
    }
}