Diagonal Sum of a Square Matrix

You are given a square matrix of integers. Write a program to calculate the sum of the diagonal elements. The main diagonal runs from the top-left to the bottom-right corner of the matrix. Input Format: The first line contains an integer n (1 <= n <= 100), the size of the matrix. Each of the next n lines contains n space-separated integers representing the elements of the matrix. Output Format: Print a single integer, the sum of the diagonal elements. Example: Input: 3 1 2 3 4 5 6 7 8 9 Output: 15