using System;

public class Program

{

    public static void Main()

    {

        int[] start = new int[11]{3,4,5,12,19,20,100,101,102,103,104};

        int[] end =  new int[21];

        int counter = 0;

        bool range = new Boolean();

        for ( int i = 1; i < end.Length;i++ )

            end[i] = 0;

        for (int i = 0; i < start.Length - 1 ; i++ ) {

            if ( start[i] + 1 == start[i + 1]) {

                if (range) 

                    continue;

                else {

                    end[counter++] = start[i];

                    range = true;

                }

            } else {

                if (!range) {

                    end[counter++] = start[i];

                }

                end[counter++] = start[i];

                range = false;

            }

        }

        end[counter++] = start[start.Length - 1];

        Console.WriteLine("[{0}]", string.Join(", ", start));

        Console.WriteLine("[{0}]", string.Join(", ", end));

        Console.WriteLine("We have {0} pairs of range", counter/2);

    }

}