using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var str = "abcdefghijklmnopqrstuvwxyz";

        var result = UniqueChars(str);

        Console.WriteLine(result);

    }

    public static bool UniqueChars(string str)

    {

        if (str.Length > 26)

            return false;

        var chars = new List<char>();

        foreach (char c in str)

        {

            if (chars.Contains(c))

                return false;

            chars.Add(c);

        }

        return true;

    }

}