using System;

using System.Diagnostics;

​

public class Program

{

    public static void Main()

    {

        var input = "This is a test";

        var result = RemoveDuplicateCharacters(input);

        Debug.Assert(string.Equals("This ae", result));

    }

    // Write a method which takes a string as an input and removes all characters which are duplicates in the string. Each character should only appear, at most, one time in the results (case insensitive).

    // Ex. This is a test -> This ae

    public static string RemoveDuplicateCharacters(string value) 

    {

        // code here...

    }

}