not 21 passes test:

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main()
        {
            var f = Console.In.ReadToEnd();
            f = f.ToLower();
            var b = f.ToCharArray();
            string c = "";
            c += b[0].ToString().ToUpper();
            for (var i = 1; i < b.Length - 3; i++)
            {
                if ((i + 1 != b.Length && (b[i] == '!' || b[i] == '?' || b[i] == '.'||b[i] == '-') && (b[i+3] != '-'&&b[i + 1] != '!' && b[i + 1] != '?' && b[i + 1] != '.')))

                {
                    c += b[i];
                    i++;
                    while (b[i] == ' ' || b[i] == '\t' || b[i] == '\r' || b[i] == '\n')
                    {
                        c += b[i];
                        if (i + 1 != b.Length)
                            i++;
                        else break;
                    }
                    c += b[i].ToString().ToUpper();
                }
                else
                    c += b[i];
            }


            Console.WriteLine(c);
        }
    }
}



not 4 passes test:

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main()
        {
            var f = Console.In.ReadToEnd();
            f = f.ToLower();
            var b = f.ToCharArray();
            string c = "";
            for (var i = 1; i < b.Length - 1; i++)
            {
                if (b[i - 1] == '-')
                    i--;
                if ((i + 1 != b.Length && i + 2 != b.Length && i + 3 != b.Length && (b[i] == '!' || b[i] == '?' || b[i] == '.' || b[i] == '-') && (b[i + 3] != '-' && b[i + 1] != '!' && b[i + 1] != '?' && b[i + 1] != '.')))
                {

                    c += b[i];
                    i++;
                    while (b[i] == ' ' || b[i] == '\t' || b[i] == '\r' || b[i] == '\n')
                    {
                        c += b[i];
                        if (i + 1 != b.Length)
                            i++;
                        else break;
                    }
                    c += b[i].ToString().ToUpper();
                }
                else
                {
                    if (i == 1)
                        c += b[i - 1].ToString().ToUpper();

                    c += b[i];
                }
            }


            Console.WriteLine(c);
        }
    }
}

Edited by author 03.01.2015 21:08

- IS IT CORRECT?
- YES, IT IS.

- Is it correct?
- Yes, it is.
Мне этот пример помог 21 тест пройти

If you have this problem - remember that a sentence is ended only with "!?."
Endline is not an end of a sentence