Matrix Diagonal Sum

Given a square matrix \(A\) of size \(n\times n\), compute the sum of its primary and secondary diagonals. The primary diagonal consists of the elements \(A[i][i]\) for \(i=0,1,\ldots,n-1\) and the secondary diagonal consists of the elements \(A[i][n-1-i]\) for \(i=0,1,\ldots,n-1\). Note that if \(n\) is odd, the center element \(A[\frac{n-1}{2}][\frac{n-1}{2}]\) is counted only once.

Input: The first line contains an integer \(n\) (the size of the matrix). Each of the next \(n\) lines contains \(n\) space-separated integers representing the matrix rows.

Output: Print a single integer that is the sum of the two diagonals of the matrix.

inputFormat

The input is read from standard input and has the following format:

n
A[0][0] A[0][1] ... A[0][n-1]
A[1][0] A[1][1] ... A[1][n-1]
...
A[n-1][0] A[n-1][1] ... A[n-1][n-1]

Where n is the size of the matrix and each line after that represents a row of the matrix.

outputFormat

Print a single integer to standard output which is the sum of the matrix's primary and secondary diagonals. If the diagonals share a common center element (in the case of an odd-sized matrix), count it only once.

3
1 2 3
4 5 6
7 8 9

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