Code
#include<bits/stdc++.h>
using namespace std;
int n, i, j, l, k, x, y, s;
int d[55][55], f[55][55][55][55];
int main() 
{
 cin>>n;
 while(cin>>x>>y>>s && x)
 d[x][y] = s;
 for(i = 1; i <= n; i++)
 for(j = 1; j <= n; j++)
 for(l = 1; l <= n; l++)
 for(k = 1; k <= n; k++) 
 {
  f[i][j][l][k] = max(max(f[i - 1][j][l - 1][k], f[i][j - 1][l][k-1]), max(f[i - 1][j][l][k - 1], f[i][j - 1][l - 1][k])) + d[i][j];
  if(i != 1 && j != k) f[i][j][l][k] += d[l][k];
  }
 printf("%d", f[n][n][n][n])
 return 0