/*
dp[i][j] := 从顶点到达点(i,j)时，所走路径上的最大值
初始化：
dp[][] = {-INF} // 测试数据有负数，所以初始值 dp[][] = -INF
dp[1][1] = arr[1][1]
状态方程：
dp[i][j] = max(dp[i-1][j-1], dp[i-1][j]) + arr[i][j]
答案：
max{ dp[N][i] }
0 <= i <= N-1
*/
1 #define _CRTDBG_MAP_ALLOC
2 #include <stdlib.h>
3 #include <crtdbg.h>
4 #define _CRT_SECURE_NO_WARNINGS
5 #define HOME
6
7 #include <iostream>
8 #include <cstdlib>
9 #include <cstdio>
10 #include <cstddef>
11 #include <iterator>
12 #include <algorithm>
13 #include <string>
14 #include <locale>
15 #include <cmath>
16 #include <vector>
17 #include <cstring>
18 using namespace std;
19 const int INF = 0x3f3f3f3f;
20 const int MaxN = 30;
21 const int Max = 110;
22
23 int N;
24 int arr[Max][Max];
25 int dp[Max][Max];
26
27 bool Check(int x, int y, int len)
28 {
29 if ((x<=0) || (y<=0) || (y>len))
30 {
31 return false;
32 }
33 return true;
34 }
35
36 void Solve()
37 {
38 int x1, y1, x2, y2;
39 dp[1][1] = arr[1][1];
40 for (int i = 1; i <= N; ++i)
41 {
42 for (int j = 1; j <= i; ++j)
43 {
44 x1 = i - 1;
45 y1 = j - 1;
46 x2 = i - 1;
47 y2 = j;
48 if (Check(x1, y1, i - 1))
49 {
50 dp[i][j] = max(dp[i][j], dp[x1][y1] + arr[i][j]);
51 }
52 if (Check(x2, y2, i - 1))
53 {
54 dp[i][j] = max(dp[i][j], dp[x2][y2] + arr[i][j]);
55 }
56 }
57 }
58 /*for (int i = 1; i <= N; ++i)
59 {
60 for (int j = 1; j <= i; ++j)
61 {
62 cout << "(" << i << "," << j << ") : " << dp[i][j] << endl;
63 }
64 }*/
65 cout << *max_element(dp[N], dp[N] + N + 1) << endl;
66 }
67
68 int main()
69 {
70 #ifdef HOME
71 freopen("in", "r", stdin);
72 //freopen("out", "w", stdout);
73 #endif
74 for (int i = 0; i < Max; ++i)
75 {
76 for (int j = 0; j < Max; ++j)
77 {
78 dp[i][j] = -INF;
79 }
80 }
81
82
83 cin >> N;
84 for (int i = 1; i <= N; ++i)
85 {
86 for (int j = 1; j <= i; ++j)
87 {
88 cin >> arr[i][j];
89 }
90 }
91 Solve();
92
93 #ifdef HOME
94 cerr << "Time elapsed: " << clock() / CLOCKS_PER_SEC << " ms" << endl;
95 _CrtDumpMemoryLeaks();
96 system("pause");
97 #endif
98 return 0;
99 }
