class Program
    {
        static void Main(string[] args)
        {
            string[] inputNum = Console.ReadLine().Split(' ');
            Console.WriteLine( CatCount(int.Parse(inputNum[0]), int.Parse(inputNum[1]) * 2)* int.Parse(inputNum[1]));
        }
        private static int CatCount (int size , int cutsize)
        {
            int count = 0;
            while (size > cutsize * (count + 1))
            {
                count++;
            }
            return count;
        }
    }