B. Odd sum

Codeforces

IDCF797B

Time1000ms

Memory256MB

Difficulty—

dpgreedyimplementation

English · Original

Chinese · Translation

Formal · Original

You are given sequence _a_1, _a_2, ..., _a__n_ of integer numbers of length _n_. Your task is to find such subsequence that its sum is odd and maximum among all such subsequences. It's guaranteed that given sequence contains subsequence with odd sum. Subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements. You should write a program which finds sum of the best subsequence. ## Input The first line contains integer number _n_ (1 ≤ _n_ ≤ 105). The second line contains _n_ integer numbers _a_1, _a_2, ..., _a__n_ ( - 104 ≤ _a__i_ ≤ 104). The sequence contains at least one subsequence with odd sum. ## Output Print sum of resulting subseqeuence. [samples] ## Note In the first example sum of the second and the fourth elements is 3.

给定一个长度为 #cf_span[n] 的整数序列 #cf_span[a1, a2, ..., an]。你的任务是找到一个子序列，使得其交错和为奇数，并且在所有满足此条件的子序列中最大。题目保证给定序列中至少存在一个交错和为奇数的子序列。子序列是指通过删除原序列中的一些元素（不改变剩余元素的顺序）而得到的序列。你需要编写一个程序，找出最优子序列的和。第一行包含整数 #cf_span[n] (#cf_span[1 ≤ n ≤ 105])。第二行包含 #cf_span[n] 个整数 #cf_span[a1, a2, ..., an] (#cf_span[ - 104 ≤ ai ≤ 104])。序列中至少包含一个交错和为奇数的子序列。请输出所求子序列的和。在第一个例子中，第二个和第四个元素的和为 #cf_span[3]。 ## Input 第一行包含整数 #cf_span[n] (#cf_span[1 ≤ n ≤ 105])。第二行包含 #cf_span[n] 个整数 #cf_span[a1, a2, ..., an] (#cf_span[ - 104 ≤ ai ≤ 104])。序列中至少包含一个交错和为奇数的子序列。 ## Output 请输出所求子序列的和。 [samples] ## Note 在第一个例子中，第二个和第四个元素的和为 #cf_span[3]。

**Definitions** Let $ n \in \mathbb{Z}^+ $ denote the length of the sequence. Let $ A = (a_1, a_2, \dots, a_n) $ be a sequence of integers, where $ a_i \in \mathbb{Z} $ and $ -10^4 \leq a_i \leq 10^4 $. **Constraints** 1. $ 1 \leq n \leq 10^5 $ 2. The sequence $ A $ contains at least one subsequence with odd sum. **Objective** Find the maximum sum $ S $ among all subsequences of $ A $ such that $ S $ is odd: $$ S = \max \left\{ \sum_{i \in I} a_i \,\middle|\, I \subseteq \{1, 2, \dots, n\},\ \sum_{i \in I} a_i \text{ is odd} \right\} $$

Samples

Input #1

4
-2 2 -3 1

Output #1

Input #2

3
2 -5 -3

Output #2

\-1

API Response (JSON)

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