using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

​

namespace FirstTask

{

    internal static class Program

    {

        private static void Main()

        {

            Console.WriteLine(TextRedactor.RedactInputMessage("ПриВеТик"));

            Console.WriteLine(TextRedactor.RedactInputMessage("Елисей"));

            Console.WriteLine(TextRedactor.RedactInputMessage("НЕ ОРИ НА МЕНЯ"));

            Console.WriteLine(TextRedactor.RedactInputMessage("чебурашка - это слишком длинно. зовите меня просто - Че!"));

            Console.WriteLine(TextRedactor.RedactInputMessage("Приффетик йа креведко"));

            Console.WriteLine(TextRedactor.RedactInputMessage("ПриФфетик ЙА Креффедко. кАк ДиЛа?"));

            Console.WriteLine(TextRedactor.RedactInputMessage("АаА."));

            Console.ReadKey();

        }

    }

​

    internal static class TextRedactor

    {

        public static string RedactInputMessage(string inputMsg)

        {

            var words = inputMsg.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);

            for (var i = 0; i < words.Length; i++)

            {

                TryToLowercaseLetters(ref words[i]);

                ReplaceLetterCombinations(ref words[i]);

            }

            СorrectСapitalLettersInSentences(ref words);

            var answer = new StringBuilder();

            foreach (var word in words)

            {

                answer.Append(word);

                answer.Append(' ');

            }

            return answer.ToString();

        }

​

        private static void TryToLowercaseLetters(ref string word)

        {

            if (char.IsUpper(word[0]) && word.Length > 1)

            {

                var countOfUpperChars = 1;

                for (var i = 1; i < word.Length; i++)

                {

                    if (char.IsUpper(word[i]))

                    {

                        countOfUpperChars++;

                    }

                }

                if (countOfUpperChars > 1 && countOfUpperChars < word.Length)

                {

                    LowercaseAllLettersInWord(ref word);

                }

            }

            else

            {

                LowercaseAllLettersInWord(ref word);

            }

        }

​

        private static void СorrectСapitalLettersInSentences(ref string[] words)

        {

            var punctuationMarks = new HashSet<char>()

            {

                '.',

                '!',

                '?'

            };

            var beginningSentenceIndex = 0;

            for (var i = 0; i < words.Length; i++)

            {

                foreach (var c in punctuationMarks)

                {

                    if (!words[i].Contains(c)) continue;

                    var curWord = words[beginningSentenceIndex];

                    words[beginningSentenceIndex] = char.ToUpper(curWord[0]) + curWord.Substring(1);

                    beginningSentenceIndex = i + 1;

                    break;

                }

            }

        }

​

        private static void ReplaceLetterCombinations(ref string word)

        {

            var letterCombinations = new Dictionary<string, string>()

            {

                ["фф"] = "в",

                ["йа"] = "я",

                ["йу"] = "ю",

                ["йо"] = "ё",

                ["ФФ"] = "В",

                ["ЙА"] = "Я",

                ["ЙУ"] = "Ю",

                ["ЙО"] = "Ё",

                ["Фф"] = "В",

                ["Йа"] = "Я",

                ["Йу"] = "Ю",

                ["Йо"] = "Ё"

            };

            foreach (var combination in letterCombinations.Keys)

            {

                if (word.Contains(combination))

                    word = word.Replace(combination, letterCombinations[combination]);

            }

        }

​

        private static void LowercaseAllLettersInWord(ref string word)

        {

            word = word.ToLower();

        }

    }

}