1 #include<iostream>
 2 using namespace std;
 3 const int maxn=30;
 4 int n,px,py;
 5 int a[maxn][maxn],f[maxn][maxn];
 6 
 7 void get_prepare()
 8 {
 9     cin >> n;
10     for (int i=0;i<n;i++)
11         for (int j=0;j<=i;j++){
12             cin >> a[i][j];
13             f[i][j]=a[i][j];
14         }
15     px=n/2;
16     py=--px;
17     for (int i=0;i<=px;i++) {if (i!=py) a[px][i]=-65536;}
18 }
19 
20 int answer()
21 {
22     for (int i=1;i<n;i++)
23         for (int j=0;j<=i;j++){
24             if (f[i-1][j]+a[i][j]>f[i][j]) f[i][j]=f[i-1][j]+a[i][j];
25             if (j-1>=0 && f[i-1][j-1]+a[i][j]>f[i][j]) f[i][j]=f[i-1][j-1]+a[i][j];
26         }
27     int max=0;
28     for (int i=0;i<n;i++) if (f[n-1][i]>max) max=f[n-1][i];
29     return max;
30 }
31 int main()
32 {
33     get_prepare();
34     cout << answer() << endl;
35     return 0;
36 }