Sum of Matrix Diagonals

Given an (N \times N) matrix, compute the sum of the elements on its two diagonals. The primary diagonal consists of elements (a_{i,i}) and the secondary diagonal consists of elements (a_{i,N-i+1}). If an element belongs to both diagonals (which occurs when (N) is odd), count it only once.

For example, consider the matrix:

( \begin{pmatrix} 1 & 2 & 3\ 4 & 5 & 6\ 7 & 8 & 9 \end{pmatrix})

The sum is computed as (1 + 5 + 9) from the primary diagonal and (3 + 5 + 7) from the secondary diagonal. Since the center element (5) is common to both, it is counted only once. Thus, the final sum is (1 + 5 + 9 + 3 + 7 = 25).

inputFormat

The first line contains an integer (N) representing the dimension of the matrix. Each of the next (N) lines contains (N) space-separated integers representing a row of the matrix.

outputFormat

Output a single integer which is the sum of the elements on both the primary and secondary diagonals.## sample

3
1 2 3
4 5 6
7 8 9

25