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

namespace Question63
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] hoge = Console.ReadLine().Trim().Split(' ').Select(x => int.Parse(x)).ToArray();
            int L = hoge[0];
            int K = hoge[1];
            int X = K * 2;
            int Z = L;
            int count = 0;
            int Ans = 0;
            do
            {
                Z = Z - X;
                count++;
                if (Z <= 0)
                {
                    count--;
                }
            }
            while (Z > 0);
            Ans = K * count;
            Console.WriteLine(Ans);
        }
    }
}