using System;

public class Program

{

        public static bool isPrime(int n)

        {

            bool res = false;

            if (n >= 2){

                res = true;

                for (int i = 2; i*i <= n; i++){

                    if (n%i == 0){

                        res = false;

                        break;

                    }

                }

            }

            return res;

        }

        public static int sumLessPrimes(int n)

        {

            int res = 0;

            for (int i = 2 ; i < n; i++)

            {

                if (isPrime(i))

                {

                    res += i;

                }

            }

            return res;              

        }

        public static void Main(string[] args)

        {

            Console.Write("Nhap n: ");

            int n = Convert.ToInt32(Console.ReadLine());

​

            Console.Write(sumLessPrimes(n));

        }

}