using System;

public class Program

{

    public static void Main()

    {

        int x = 2, y = 2, z = 0, N, S=0;

            Console.WriteLine("Nhap N:");

            N = int.Parse(Console.ReadLine());

            if (N == 0 | N == 1 | N == 2)

            {

                Console.WriteLine($"Khong tim duoc trung binh cong cua cac so nguyen to nho hon {N}");

            }

            else

            {

                while (x < N)

                {

                    while (y <= x)

                    {

                        if (x % y == 0 & y < x)

                        {

                            y = x;

                        }

                        else if (y == x)

                        {

                            S = S + x;

                            z = z + 1;

                        }

                        y++;

                    }

                    x++;

                    y = 2;

                }

                Console.WriteLine($"Trung binh cong cua cac so nguyen to nho hon {N} la {1.0 * S / z}");

            }

            Console.ReadLine();

    }

}