using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Capitalize(null) == null);

        Console.WriteLine(Capitalize("-") == "-");

        Console.WriteLine(Capitalize("y") == "Y");

        Console.WriteLine(Capitalize("yo") == "Yo");

        Console.WriteLine(Capitalize("yoo") == "Yoo");

        Console.WriteLine(Capitalize("Y") == "Y");

        Console.WriteLine(Capitalize("Yo") == "Yo");

        Console.WriteLine(Capitalize("Yoo") == "Yoo");

        Console.WriteLine(Capitalize("YoY") == "Yoy");

        Console.WriteLine(Capitalize("Y M C A") == "Y M C A");

        Console.WriteLine(Capitalize("Yo mama Cuts apple") == "Yo Mama Cuts Apple");

        Console.WriteLine(Capitalize("Y-M C-A") == "Y-M C-A");

        Console.WriteLine(Capitalize("Yo-mama Cuts-apple") == "Yo-Mama Cuts-Apple");

        Console.WriteLine(Capitalize("Yo2o") == "Yo2O");

        Console.WriteLine(Capitalize("MENÉNDEZ MENÉNDEZ Yoh") == "Menéndez Menéndez Yoh");

        Console.WriteLine(Capitalize("STØRMER John") == "Størmer John");

    }

​

    public static string Capitalize(string input)

    {

        if (string.IsNullOrWhiteSpace(input))

            return null;

        var result = new List<char>{char.ToUpper(input[0])};

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

        {

            result.Add(char.IsLetter(input[i]) && !char.IsLetter(input[i - 1])

                ? char.ToUpper(input[i])

                : char.ToLower(input[i]));

        }

        return string.Concat(result);

    }

}