using System;
using System.Linq;

namespace yukicoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            int[,] F = new int[n, n];
            bool[] used = new bool[n];
            int max = -1;
            int ans = 0;
            int ii = 0;
            int jj = 0;
            for (int i = 0; i < n; i++)
            {
                string[] lines = Console.ReadLine().Split(' ');
                for (int j = 0; j < n; j++)
                {
                    F[i, j] = int.Parse(lines[j]);
                }
            }
            while (used.Any(b => b == false))
            {
                max = -1;
                for (int i = 0; i < n; i++)
                {
                    if (used[i])
                    {
                        continue;
                    }
                    for (int j = 0; j < n; j++)
                    {
                        if (used[j])
                        {
                            continue;
                        }
                        if (max < F[i, j])
                        {
                            max = F[i, j];
                            ii = i;
                            jj = j;
                        }
                    }
                }

                used[ii] = true;
                used[jj] = true;
                ans += max;
            }
            Console.WriteLine(ans);
        }
    }
}