using System.Collections.Generic;

using System.Linq;

using static System.Console;

using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        var result = Transform("aaaaa");

        result.ToList().ForEach(WriteLine);

    }

    public static IEnumerable<string> Transform(string str)

    {

        var result = new StringBuilder(str.ToLower()); 

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

        { 

            result[i] = char.ToUpper(str[i]);

            yield return result.ToString();

            result[i] = char.ToLower(str[i]);

        }

    }

}