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

    namespace lecture
    {
    class Program
        {
        public static void Main(String[] args)
            {
            int[] tmp = Console.ReadLine().Trim().Split(' ').Select(x => int.Parse(x)).ToArray();
            int L = tmp[0];
            int K = tmp[1];
            int X = K * 2;
            int Z = L;
            int count = 0;
            int Ans = 0;
            do
            {
                if ((Z != 0) || (Z >= 1))
                {
                    Z = Z - X;
                    count++;
                    if (Z <= 0)
                    {
                        count--;
                    }
                }

            }
            while (Z > 0);
            Ans = K * count;
            Console.WriteLine(Ans);

        }
    }
}