using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace ConsoleApp3

{

    class Program

    {

        static void Main(string[] args)

        {

            int n;

            Console.WriteLine("nhập n: ");

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

​

            TongCacSoNT(n);

        }

​

        static int TongCacSoNT(int n)

        {

            int count = 0;

​

            for (int i = 1; i <= n; i++)

            {

                if(LaSoNguyenTo(i) == true)

                {

                    count += i;

                }                

            }

            return count;

        }

​

        static bool LaSoNguyenTo(int n)

        {

            int count = 0;

            for (int i = 1; i <= Math.Sqrt(n); i++)

            {

                if(n % i == 0)

                {

                    count++;

                }

            }

            if (count == 1) return true;

            else return false;

        }

    }

}

​