using System;

using System.Collections.Generic;                   

public class Program

{

    public static bool isPrime(int number){

        if (number == 1) return true;

        if (number == 2) return true;

        for(int check =2; check<number; check++) {

            if(number%check==0) {

                return false;

            }

        }

        return true;

    }

​

    public static void removeAllPrime(List<int> list) {

            for(int j = list.Count-1; j>=0; j--) { 

            if (isPrime(list[j]))

                list.Remove(list[j]);

            }   

        }

​

    public static void Main()

    {

        List<int> list = new List<int>();

        Console.WriteLine("Please input integers: (in one line)");

        string input = Console.ReadLine();

        string[] tokens = input.Split();   // split string into tokens "12 13 10" -> "12" "13" "10"

        foreach (string s in tokens) {

            int num;

            bool success = int.TryParse(s,out num);  // TryParse returns true if successfully converted s into an int 

                                                     // the converted int is put into the second parameter using keyword "out"  

                                                     // do you know why "out" is used here? why not return the converted integer?

            if (success) {

                list.Add(num);    // add num to list if success

            } 

        }

        removeAllPrime(list);

​

        Console.WriteLine(String.Join(",", list));

​

    }

​

}