3. Diagonal Difference

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DiagonalDifference
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());

            long[][] matrix = new long[n][];
            // Filling the Matrix
            for (int row = 0; row < n; row++)
            {
                matrix[row] = Console.ReadLine().Split().Select(long.Parse).ToArray();
            }

            // Sum the first diagonal of Matrix
            long firstDiagonalSum = 0;
            for (int row = 0; row < n; row++)
            {
                for (int col = 0; col < n; col++)
                {
                    if (row == col)
                    {
                        firstDiagonalSum += matrix[row][col];
                    }
                }
            }

            // Sum the second diagonal of Matrix
            long secondDiagonalSum = 0;
            for (int row = 0; row < n; row++)
            {
                for (int col = n - 1; col >= 0; col--) 
                {
                    if (col == Math.Abs(row - n + 1))
                    {
                        secondDiagonalSum += matrix[row][col];
                    }
                }
            }
            //Console.WriteLine(firstDiagonalSum);
            //Console.WriteLine(secondDiagonalSum);
            Console.WriteLine(Math.Abs(firstDiagonalSum - secondDiagonalSum));
        }
    }
}