#include<bits/stdc++.h>

using namespace std;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());


int main()
{
  int n;
  scanf("%d", &n );

  vector< vector< int > > w( n, vector< int> ( n ) );
  for( int i = 0; i < n; ++ i )
    for( int j = 0; j < n; ++ j )
      scanf("%d", &w[i][j] );

  double ans = 0.0;
  auto score = [&]( vector< double > &e )
  {
    double sc = 0;

    for( int i = 0; i < n; ++ i )
      for( int j = i + 1; j < n; ++ j )
        sc += 1.0 * e[i] * e[j] * w[i][j];

    ans = max( ans, sc );
    return sc;
  };

  uniform_int_distribution<int> dis(0, n - 1);

  vector< double > e ( n, 1.0 / n );

  while( 1.0 * clock() / CLOCKS_PER_SEC < 0.9 )
  {
    int x = dis( rng ), y = dis( rng );
    if( x == y ) continue;

    const double sum = e[x] + e[y];

    double low = 0.0, high = sum;
    for( int it = 0; it < 100; ++ it )
    {
      const double x1 = low + ( high - low ) / 3.0L;
      auto e1 = e;
      e1[x] = x1, e1[y] = sum - x1;

      const double x2 = high - ( high - low ) / 3.0L;
      auto e2 = e;
      e2[x] = x2, e2[y] = sum - x2;

      if( score( e1 ) > score( e2 ) )
        high = x2;
      else
        low = x1;
    }
    
    e[x] = low, e[y] = sum - low;
  }

  printf("%0.12f\n", ans );
  return 0;
}