using System;

public class Program

{

    public static void Main()

    {

        DateTime then = DateTime.Now;

        Console.WriteLine(how_many_primes(25000).ToString());

        Console.WriteLine($"Took {DateTime.Now - then}");

    }

    static int is_prime(int n) 

    {

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

            if (n % i == 0) { return 0;}

        }

        return 1;

    }

    static int how_many_primes(int p_limit) 

    {

        int numPrimes = 0;

        for (int i = 2; i < p_limit; ++i) {

            numPrimes += is_prime(i) ;

        }

        return numPrimes;

    }

}