#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 510;

int d[N][N];
int g[N][N];
int n;

int dfs(int x, int y)
{
    if(d[x][y] != -1e8)
        return d[x][y];

    if(x == n - 1)
        return g[x][y];

    int dx[] = {1, 1}, dy[] = {0, 1};

    for(int i = 0; i < 2; i ++)
    {
        int xx = x + dx[i], yy = y + dy[i];

        if(xx < n)
            d[x][y] = max(d[x][y], g[x][y] + dfs(xx, yy));
    }

    return d[x][y];//记得返回
}

int main()
{
    cin >> n;

    for(int i = 0; i < n; i ++)
        for(int j = 0; j <= i; j ++)
        {
            cin >> g[i][j];
            d[i][j] = -1e8;//d数组不能初始化为-1因本题中数字可为-1
        }

    dfs(0, 0);

    cout << d[0][0];
}