CF177A2 Good Matrix Elements

The Smart Beaver from ABBYY got hooked on square matrices. Now he is busy studying an $ n×n $ size matrix, where $ n $ is odd. The Smart Beaver considers the following matrix elements good: - Elements of the main diagonal. - Elements of the secondary diagonal. - Elements of the "middle" row — the row which has exactly  rows above it and the same number of rows below it. - Elements of the "middle" column — the column that has exactly  columns to the left of it and the same number of columns to the right of it.  The figure shows a $ 5×5 $ matrix. The good elements are marked with green. Help the Smart Beaver count the sum of good elements of the given matrix.

The first line of input data contains a single odd integer $ n $ . Each of the next $ n $ lines contains $ n $ integers $ a_{ij} $ $ (0

Print a single integer — the sum of good matrix elements.

In the first sample all matrix elements will be good. Good elements in the second sample are shown on the figure.