using System;

public class Program

{

    public static void Main()

    {

        string testString = "AN UPERCASE TEST STRING! HERE ARE SOME MORE WORDS";

        Console.WriteLine(FirstLetterOfWordToLowercase(testString));

        Console.WriteLine(LastLetterOfWordToLowercase(testString));

        Console.WriteLine(FirstAndLastLetterOfWordToLowercase(testString));

    }

    private static string FirstAndLastLetterOfWordToLowercase(string stringToTransform)

    {

        char[] stringCharacters = stringToTransform.ToCharArray();

        for (int charIndex = 0; charIndex < stringCharacters.Length; charIndex++)

        {

            char currentCharacter = stringCharacters[charIndex];

            if (!isWordSepparator(currentCharacter))

            {

                if (charIndex == 0 || charIndex == stringCharacters.Length -1 || (charIndex > 0 && isWordSepparator(stringCharacters[charIndex - 1])) || isWordSepparator(stringCharacters[charIndex +1]))

                {

                    stringCharacters[charIndex] = char.ToLower(currentCharacter);

                }

            }

        }

        return new string(stringCharacters);

    }

    private static string FirstLetterOfWordToLowercase(string stringToTransform)

    {

        char[] stringCharacters = stringToTransform.ToCharArray();

        for (int charIndex = 0; charIndex < stringCharacters.Length; charIndex++)

        {

            char currentCharacter = stringCharacters[charIndex];

            if (!isWordSepparator(currentCharacter))

            {

                if (charIndex == 0 || (charIndex > 0 && isWordSepparator(stringCharacters[charIndex - 1])))

                {

                    stringCharacters[charIndex] = char.ToLower(currentCharacter);

                }

            }

        }

        return new string(stringCharacters);

    }

    private static string LastLetterOfWordToLowercase(string stringToTransform)

    {

        char[] stringCharacters = stringToTransform.ToCharArray();

        for (int charIndex = 0; charIndex < stringCharacters.Length; charIndex++)

        {

            char currentCharacter = stringCharacters[charIndex];

            if (!isWordSepparator(currentCharacter))

            {

                if (charIndex == stringCharacters.Length -1 || isWordSepparator(stringCharacters[charIndex +1]))

                {

                    stringCharacters[charIndex] = char.ToLower(currentCharacter);

                }

            }

        }

        return new string(stringCharacters);

    }

    private static bool isWordSepparator(char character)

    {

        return char.IsPunctuation(character) || char.IsSeparator(character);

    }

}