Sum Frame of a Matrix T54397

Let $M$ be a square matrix $N \times N$. This matrix has different frames. Frame $0$ is formed by rows $0$ and $N-1$ and columns $0$ and $N-1$. Frame $1$ is formed by rows $1$ and $N-2$ and columns $1$ and $N-2$, excluding the parts that are part of frame $0$, etc.

In the following example, you have that the frame $0$ is formed by all the positions where there is a $0$, the frame $1$ the positions where there is a $1$, and the frame $2$ the positions where there is a $2$:

                          0  0  0  0  0
                          0  1  1  1  0
                          0  1  2  1  0
                          0  1  1  1  0
                          0  0  0  0  0

You must implement the function int sumaMarc(const Matriu& m, int x); with the following specification:

PRE: $m$ a matrix $N \times N$ and $0 \leq x < N/2 + (N~mod~2)$.

POST: Returns the sum of the elements of the frame $x$ of $M$.

Observation

You only need to send the function we ask for and the functions you define. The rest will be ignored.

Input

A matrix $N \times N$ and $0 \leq x < N/2 + (N~mod~2)$.

Output

The sum of the elements of the frame $x$ of $M$.