SumPrimeNonPrime 1

using System;

namespace SumPrimeNonPrime
{
    class SumPrimeNonPrime
    {
        static void Main()
        {

            string input = Console.ReadLine();
            int N = int.Parse(input);
            int nativeSum = 0;
            int nonNativeSum = 0;

            while (input != "stop")
            {

                if (N < 3)
                {
                    if (N == 2)
                    {
                        nativeSum += N;
                    }
                    else
                    {
                        nonNativeSum += N;
                    }
                }
                else
                {
                    if (N % 2 == 0)
                    {
                        nonNativeSum += N;
                    }
                    else
                    {
                        int div;

                        for (div = 3; N % div != 0; div += 2)
                            ;

                        if (div == N)
                        {

                            nativeSum += N;
                        }
                        else
                        {
                            nonNativeSum += N;
                        }
                    }
                }

                input = Console.ReadLine();
                if (input == "stop")
                {
                    break;
                }
                else
                {
                    N = int.Parse(input);
                }
                if (N < 0)
                {
                    Console.WriteLine("Number is negative.");
                    input = Console.ReadLine();
                    N = int.Parse(input);
                }
            }
            Console.WriteLine($"Sum of all prime numbers is: {nativeSum}");
            Console.WriteLine($"Sum of all non prime numbers is: {nonNativeSum}");
        }
    }
}