using System;

using System.Collections.Generic;

using System.Collections;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Console.WriteLine(IsUnique(""));

        Console.WriteLine(IsUnique("abcdef"));

        Console.WriteLine(IsUnique("asdfasdf"));

    }

    public static bool IsUnique(String str) {

        var ht = new Hashtable();

        foreach(var character in str.ToCharArray())

        {

            if (ht.ContainsKey(character)) {

                return false;

            }

            else {

                ht.Add(character, 1);

            }

        }

        return true;

    }

}