using System;

using System.Text.RegularExpressions;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        var input2 = @"\u0410\u041b\u0415\u041a\u0421\u0410\u041d\u0414\u0420";

        var result = Regex.Replace(

            input2,

            @"\\[Uu]([0-9A-Fa-f]{4})",

            m => char.ToString(

            (char)ushort.Parse(m.Groups[1].Value, NumberStyles.AllowHexSpecifier)));

        Console.WriteLine(result);

    }

}