Diagonals

In the square table $n\cdot n$ find the sum of integers at the main and the secondary diagonals.

Input

The first line contains the size $n(1\le n\le 500)$ of the matrix. The next lines describe a matrix $n\cdot n$. The elements of the matrix are not greater than $10^5$ by absolute value.

Output

Print the sum of the integers at the main and the secondary diagonals.

Examples