Operations on a Stack

AtCoder

IDarc194_a

Time2000ms

Memory256MB

Difficulty—

You are given an integer sequence of length $N$: $(A_1, A_2, \ldots, A_N)$. There is also a sequence $S$, which is initially empty. For each $i = 1, 2, \ldots, N$ in this order, you perform exactly one of the following two operations: * Append $A_i$ as an element to the end of $S$. * Delete the last element of $S$. You cannot choose this operation if $S$ is empty. Print the maximum possible value of the sum of the elements of $S$ after all operations. ## Constraints * $1 \leq N \leq 2 \times 10^5$ * $-10^9 \leq A_i \leq 10^9$ * All input values are integers. ## Input The input is given from Standard Input in the following format: $N$ $A_1$ $A_2$ $\ldots$ $A_N$ [samples]

Samples

Input #1

6
3 -1 -4 5 -9 2

Output #1

8

Starting from the initial state where $S$ is an empty sequence, consider the following operations:

*   For $i = 1$, append $A_1 = 3$ to the end of $S$. Now, $S = (3)$.
*   For $i = 2$, append $A_2 = -1$ to the end of $S$. Now, $S = (3, -1)$.
*   For $i = 3$, delete the last element of $S$. Now, $S = (3)$.
*   For $i = 4$, append $A_4 = 5$ to the end of $S$. Now, $S = (3, 5)$.
*   For $i = 5$, append $A_5 = -9$ to the end of $S$. Now, $S = (3, 5, -9)$.
*   For $i = 6$, delete the last element of $S$. Now, $S = (3, 5)$.

Here, the sum of the elements of $S$ after all operations is $3 + 5 = 8$, which is the maximum possible value.

Input #2

1
-1

Output #2

\-1

Note that if $S$ is empty, you must choose to append an element.

Input #3

20
-14 74 -48 38 -51 43 5 37 -39 -29 80 -44 -55 59 17 89 -37 -68 38 -16

Output #3

API Response (JSON)

{
  "problem": {
    "name": "Operations on a Stack",
    "description": {
      "content": "You are given an integer sequence of length $N$: $(A_1, A_2, \\ldots, A_N)$. There is also a sequence $S$, which is initially empty. For each $i = 1, 2, \\ldots, N$ in this order, you perform exactly on",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "arc194_a"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "You are given an integer sequence of length $N$: $(A_1, A_2, \\ldots, A_N)$. There is also a sequence $S$, which is initially empty.\nFor each $i = 1, 2, \\ldots, N$ in this order, you perform exactly on...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments