Matrix Diagonal Sum

Given a square matrix \( A \) of size \( n \times n \), your task is to compute the sum of the elements on its main diagonal. The main diagonal of a matrix consists of the elements \( A_{i,i} \) for \( i = 1, 2, \dots, n \).

Example:

Input:
3
1 2 3
4 5 6
7 8 9
Output:
15

</p>

In the above example, the main diagonal elements are 1, 5, and 9, and their sum is \( 1+5+9=15 \).

inputFormat

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

• The first line contains a single integer \( n \) which represents the size of the matrix.
• The next \( n \) lines each contain \( n \) space-separated integers representing the rows of the matrix.

outputFormat

Print a single integer to standard output, which is the sum of the elements along the main diagonal of the matrix.

## sample

3
1 2 3
4 5 6
7 8 9

15