Problem 2240. Sum the 'edge' values of a matrix

Sum the 'edge' values of an input matrix (the values along the perimeter).

Example

 [1 2 3
  4 5 6
  7 8 9]

Output = 1 + 2 + 3 + 6 + 9 + 8 + 7 + 4 = 40;

Assumption: Input matrix equal or bigger than 3x3.