using System;

public class Program

{

    static bool stt(string exp)

        {

                        int[] count = new int[256];

        for( int i = 0; i< exp.Length; i++)

        {

            count[exp[i]]++;

        if (count[exp[i]] > 1)

        {

            //Console.WriteLine("String does not have unique characters;");

            return false;

        }

​

        }

             return true;

    }

    public static void Main()

    {       

        string tt = "helpo";

        Console.WriteLine(stt(tt));

    }

}