using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            List<int> primes = new List<int>();
            primes.Add(2);
            Console.Write("Calculate primes up to : ");
            int n = int.Parse(Console.ReadLine());
            bool isPrime = true;

            for (int i = 3; i <= n; i += 2) // can't be prime if even number > 2
            {
                for (int j = 0; j < primes.Count; j++)
                {
                    if (i % primes[j] == 0) 
                    {
                        isPrime = false;
                        break;
                    }
                }
                if (isPrime)
                {
                    primes.Add(i);
                }
                else
                {
                    isPrime = true;
                }
            }

            // print them out
            Console.WriteLine();
            foreach (int prime in primes) Console.Write("{0,3} ", prime);
            Console.WriteLine();
            Console.ReadKey();
        }
    }
}