Inserting into Array (C#)

Question

I am trying to insert an int value in int array at the user input index and getting an error ( Index was outside the bounds of the array ).

 Console.WriteLine("Enter the length of Linear Array");

            int length = Convert.ToInt32(Console.ReadLine());

            int[] LinearArr = new int[length];

            Console.WriteLine("Maximum number of input : {0}",length);

            for (int i = 0; i < LinearArr.Length; i++)

            {

                LinearArr[i] = Convert.ToInt32(Console.ReadLine());

            }

            Console.WriteLine("What number you want to insert and at what index");

            int InsertNum = Convert.ToInt32(Console.ReadLine());

            int k = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Number :{0} and Index :{1}",InsertNum,k);

            while (length>=k)

            {

                LinearArr[length + 1] = LinearArr[length];

                length = length - 1;

            }

            LinearArr[k] = InsertNum;

            length = length + 1;

            Console.ReadLine();