C#: Enter the integer n has 4 digits. Looking for big numbers second.

//Enter the integer n has 4 digits. Looking for big numbers second.
//Example: n=2071. The number big number second is 2
Source code:

class Program{

        static void Main(){           

            int n;

            int[] arr = new int[4];

            do

            {

                Console.Write("Input n has 4 digits: ");

                n = int.Parse(Console.ReadLine());

            } while (n < 1000 || n > 9999);           

            for (int i = 0; i < 4; i++){

                arr[i] = n % 10;

                n = n / 10;

            }

            for (int i = 0; i < 3; i++)

                for (int j = i+1; j < 4;j++)

                    if (arr[i] => arr[j]){

                        int temp = arr[i];

                        arr[i] = arr[j];

                        arr[j] = temp;

                    }            

            Console.WriteLine("The second big number is: {0}", arr[2]);   

            Console.ReadLine();

        }

}