using System;

public class Program

{

    public static int SumEven(int n)

        {

     if (n < 2)

        {

            return 0;

        }

     if (n % 2 == 0)

        {

            return n + SumEven(n - 2);

        }

        else

        {

            return SumEven(n - 1);

        }

    }

    public static void Main()

    {

        Console.WriteLine(SumEven(7));

    }

}