#include<bits/stdc++.h>
using namespace std;

int triangle[101][101] = {0};
long maxPathSum[101][101][201] = {0};


int getParity(int n) {
    if(n % 2)
        return -1;
    return 1;
}

void solve(){
    int i, j, k;
    int n;
    // take input trinagle
    cin>>n;
    for(i = 0; i < n; i++) {
        for(j = 0; j <= i; j++) {
            cin>>triangle[i][j];
        }
    }

    // solution
    if(n%2)
        n--;
    int maxPathParity = 2*n;
    int parity;
    for(j = 0; j < n; j++) {
        parity = getParity(triangle[n-1][j]);
        maxPathSum[n-1][j][n + parity] = triangle[n-1][j];
    }
    for(i = n-2; i >= 0; i--) {
        for(j = 0; j <= i; j++) {
            int currElement = triangle[i][j];
            int parity = getParity(currElement);
            for(k = 0; k <= maxPathParity; k++) {
                if(k - parity >= 0 && k - parity <= maxPathParity) {
                    long pathDown = maxPathSum[i + 1][j][k - parity];
                    long pathBottomRight = maxPathSum[i + 1][j + 1][k - parity];
                    long maxPath = max(pathDown, pathBottomRight);
                    maxPathSum[i][j][k] = max(maxPathSum[i][j][k],
                                        currElement + maxPath);
                }
            }
        }
    }
    long ans = maxPathSum[0][0][n];

    cout<<ans<<endl;

}

int main(){
    solve();

    return 0;
}