Write a C# program to compute the sum of the first 500 prime numbers

using System;  
public class Exercise26
{  
    public static void Main() 
      {     
          Console.WriteLine("\nSum of the first 500 prime numbers: ");
           long sum = 0;
            int ctr = 0;
            int n = 2;
            while (ctr < 500)
              {
                if (isPrime(n))
                {
                    sum += n;
                    ctr++;
                }
                n++;
            }

            Console.WriteLine(sum.ToString());
                    
    }
     public static bool isPrime(int n)
        {
            int x = (int)Math.Floor(Math.Sqrt(n));

            if (n == 1) return false;
            if (n == 2) return true;

            for (int i = 2; i <= x; ++i)
            {
                if (n % i == 0) return false;
            }

            return true;
        }
}