using System;

public class Program

{

    public static void Main()

    {

        int N=5;

        int a=2;

        int x;

        if (N<2)

        {

            Console.WriteLine($"{N} khong phai la so nguyen to");

        }

        else if (N==2)

            {

                Console.WriteLine($"{N} la so nguyen to");

            }

            else                

            {

                while (a < N)

                    {

                    x=N%a;

                    if (x!=0)

                        {

                        Console.WriteLine($"{N} la so nguyen to");

                        }

                    a++;

                    }   

            }

​

        }

    }

​