практикум 5 II. 4

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace практикум5_II
{
    class Program
    {
        static bool PrimeNumber(int n)
        {
            for (int i = 2; n >= i * i; i++)
            {
                if (n % i == 0)
                {
                    return false;
                }
            }
                return true;
        }
        static void Main(string[] args)
        {
            Console.Write("Enter number: ");
            int n = int.Parse(Console.ReadLine());

            for (int i = n - 1; i > 2; i--)
            {
                if (PrimeNumber(i))
                {
                    Console.WriteLine("{0}", i);
                    break;
                }
            }
                if (n == 1 || n == 2 || n == 3)
                    Console.WriteLine("there is not prime number less then {0}", n);
        }
    }
}