Sum prime and nonprime numbers

using System;

public class Program
{
	public static void Main()
	{
		string input = Console.ReadLine();
            int sumPrime = 0;
            int sumNonprime = 0;

            while (input != "stop")
            {

                int num = int.Parse(input);
                int count = 0;

                for (int i = 2; i <= Math.Sqrt(num); i++)
                {

                    if (num % i == 0)
                    {
                        count++;
                        break;
                    }

                }

                if (num < 0)
                {
                    Console.WriteLine("Number is negative.");
                }
                else if (count > 0 || num == 1)
                {
                    sumNonprime += num;
                }
                else
                {
                    sumPrime += num;
                }

                input = Console.ReadLine();


            }

            Console.WriteLine("Sum of all prime numbers is: {0}", sumPrime);
            Console.WriteLine("Sum of all non prime numbers is: {0}", sumNonprime);

	}
}