A column diagram is composed of n consecutive columns arranged in a horizontal row. Each column has a width of 1, and the base of each column is on the x-axis. The heights of the columns are given in the int a, where a[i] is the height of the i-th column. The picture below shows an example of a column diagram:
Return the perimeter of the given column diagram.
|-||a will contain between 1 and 50 elements, inclusive.|
|-||Each element of a will be between 1 and 50, inclusive.|