public static void Main()
Console.WriteLine("\nSum of the first 500 prime numbers: ");
Console.WriteLine(sum.ToString());
public static bool isPrime(int n)
int x = (int)Math.Floor(Math.Sqrt(n));
if (n == 1) return false;
for (int i = 2; i <= x; ++i)
if (n % i == 0) return false;