using System;

using System.Text;

using System.Text.RegularExpressions;

using System.Linq;

using System.IO;

public class Program

{

    /*

    Input      Output:

bad        bBaAdD

Nice       NniIcCeE

T e S t    Tt eE Ss tT

s E t      sS Ee tT

1!1!1st!   1!1!1sStT!

n00b       nN00bB     

(e.g.)     (eE.gG.)

H3l|@!     Hh3lL|@!

*/

    public static void Main()

    {

        Func<string, string> f=

            s=>string.Concat(s.Select(c=>c+(char.IsLetter(c)?(char)(c^32)+"":"")));

        Console.WriteLine(f3(f("bad")));

        Console.WriteLine(f3(f("Nice")));

        Console.WriteLine(f3(f("T e S t")));

        Console.WriteLine(f3(f("H3l|@!")));

        Console.WriteLine(f3(f("(e.g.)")));

        Console.WriteLine(f3("aAa")); // aa

        Console.WriteLine(f3("aA")); // a

        Console.WriteLine(f3("Aaa")); // Aa

        Console.WriteLine(f3("aaaAAA")); // aaaAA

        Console.WriteLine(f3("AA")); // AA

        Console.WriteLine(f3("AB")); // AB

        /*

        Console.WriteLine(f4(f("bad")));

        Console.WriteLine(f4(f("Nice")));

        Console.WriteLine(f4(f("T e S t")));

        Console.WriteLine(f4(f("H3l|@!")));

        Console.WriteLine(f4(f("(e.g.)")));

        Console.WriteLine(f4("aAa")); // aa

        Console.WriteLine(f4("aA")); // a

        Console.WriteLine(f4("Aaa")); // Aa

        Console.WriteLine(f4("aaaAAA")); // aaaAA

        Console.WriteLine(f4("AA")); // AA

        Console.WriteLine(f4("AB")); // AB

        */

    }

    static string f2(string s)

    {

        var r = "";

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

        {

            r+=s[i];

            if (char.IsLetter(s[i]) & i+1 < s.Length)

                if (char.ToLower(s[i]) == char.ToLower(s[i + 1])

                  & char.IsLower(s[i]) != char.IsLower(s[i + 1]))

                    i += 1;

        }

        return r;

    }

    static string f3(string s)

    {

        var r="";for(int i=0,l=s.Length;i<l;i++){var c=s[i];r+=c;

            if(char.IsLetter(c)&i+1<l&&(c|32)==(s[i+1]|32)&c!=s[i+1])i++;}return r;

    }

    static string f4 (string s)

    {

        return Regex.Replace(s,@"(.)(?!\1)(?i)\1",m=>(m+"")[0]+"");

    }

}