/*
欧拉计划第 67 题, DP,滑雪, 同第 18 题。
answer: 7273
*/
#include<bits/stdc++.h>
using namespace std;
const int N = 1000;
int d[N][N];
int ans[N][N], n = 100;
int main(void)
{
for (int i = 1; i <= n; ++ i)
for (int j = 1; j <= i; ++ j)
{
cin >> d[i][j];
ans[i][j] = max(ans[i-1][j-1], ans[i-1][j]) + d[i][j];
}
int v = 0;
for (int i = 1; i <= n; ++ i) v = max(v, ans[n][i]);
cout << v << endl;
return 0;
}