using System;
using System.Linq;

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

            var matrix = new int[size, size];
            int primaryDiagonalSum = 0;

            for (int row = 0; row < size; row++)
            {
                var numbers = Console.ReadLine()
                .Split(new char[] { ',', ' ' }, StringSplitOptions.RemoveEmptyEntries)
                .Select(int.Parse)
                .ToArray();

                for (int col = 0; col < size; col++)
                {
                    matrix[row, col] = numbers[col];
                    if (row == col)
                    {
                        primaryDiagonalSum += matrix[row, col];
                    }
                }
            }

            Console.WriteLine(primaryDiagonalSum);

		 }
    }
}