#include <iostream>
using namespace std;
const int N =110;
int f[N][N];
int a[N][N];
int n;
int main()
{
    cin >> n;
    for (int i = 1 ,k = -(n/2); i <= n ; i ++, k ++)
       for (int j = 1 ; j <= i ; j ++)
       {
           cin >> a[i][j];
           if (j <= k || j > i - k) a[i][j] = 0;
       }
    for (int i = 1 ; i <= n ; i ++)  f[n][i] = a[n][i];

    for (int i = n - 1 ; i ; i --)
       for (int j = 1 ; j <= i ; j ++)
       {
           f[i][j] = max(f[i + 1][j] + a[i][j], f[i + 1][j + 1] + a[i][j]);
       }
    cout << f[1][1] << endl;
    return 0;
}