using System;

using System.Collections.Generic;

public class Program

{

    private static readonly char[] possibleChoices = new char[] { '0', '1' };

    public static void Main(string[] args)

    {

        List<string> binaries = new List<string>();

        PrintBinary(2, string.Empty, binaries);

        Console.WriteLine(string.Join(", ", binaries));

    }

    private static void PrintBinary(int n, string str, List<string> binaries)

    {

        // Console.WriteLine($"str: {str}");

        if (str.Length == n)

        {

            binaries.Add(str);

            return;

        }

        foreach (char c in possibleChoices)

        {

            // choose

            str = string.Concat(str, c);

            // Recurse

            PrintBinary(n, str, binaries);

            // Revert

            str = str.Remove(str.Length - 1, 1);

        }

    }

}