PrimeNonPrimeSums

using System;

namespace SumPrimeNonPrimeNums
{
    class Program
    {
        static void Main(string[] args)
        {

            string input = (Console.ReadLine());
            int primeSum = 0;
            int nonPrimeSum = 0;

            while(input != "stop")
            {
                int num = int.Parse(input);
                var boundary = (int)Math.Floor(Math.Sqrt(num));

                if (num < 0)
                    Console.WriteLine("Number is negative.");
                else if (num <= 1)
                    nonPrimeSum += num;
                else if (num == 2)
                    primeSum += num;
                else if (num % 2 == 0)
                    nonPrimeSum += num;
                else
                {
                    bool isPrime = true;
                    for (int i = 3; i <= boundary; i += 2)
                        if (num % i == 0)
                            isPrime = false;
                    if (isPrime)
                    {
                        primeSum += num;
                    }
                    else
                    {
                        nonPrimeSum += num;
                    }
                }
                input = Console.ReadLine();
            }

            Console.WriteLine($"Sum of all prime numbers is: {primeSum}");
            Console.WriteLine($"Sum of all non prime numbers is: {nonPrimeSum}");
        }
    }
}