Sum of Special Diagonal

You are given an n x n matrix. Your task is to calculate the sum of the elements along the special diagonal, which is the diagonal from the top-left corner to the bottom-right corner.

Formally, given a matrix \(A\) of size \(n \times n\), compute the value:

[ S = \sum_{i=0}^{n-1} A_{i,i} ]

Input will be provided from the standard input (stdin) and output should be printed to the standard output (stdout).

Note: The matrix is guaranteed to be square.

inputFormat

The input begins with an integer \(n\) representing the size of the matrix. The next \(n\) lines each contain \(n\) space-separated integers representing the rows of the matrix.

Example:

3
1 2 3
4 5 6
7 8 9

outputFormat

Output a single integer which is the sum of the elements on the special (main) diagonal.

For the sample input above, the output should be:

15

## sample

3
1 2 3
4 5 6
7 8 9

15

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