class Program
    {
        static void Main(string[] args)
        {
            string[] inputNum = Console.ReadLine().Split(' ');

            int count = 0;
            while (int.Parse(inputNum[0]) > int.Parse(inputNum[1]) * 2 * (count+1))
            {
                count++;
            }
            Console.WriteLine( count* int.Parse(inputNum[1]));
        }
    }