In the square table n × n find the sum of integers at the main and at the secondary diagonal.

Input

First line contains the size n (1 ≤ n ≤ 500) of the matrix. Next lines describe a matrix n × n. The elements of the matrix are not greater than 105 by absolute value. To understand how each diagonal is called, look at the second sample.

Output

Print the sum of integers at main and secondary diagonal.