题目描述
Given is an integer sequence A_1, ..., A_N of length N.
We will choose exactly $\left\lfloor \frac{N}{2} \right\rfloor$ elements from this sequence so that no two adjacent elements are chosen.
Find the maximum possible sum of the chosen elements.
Here $\lfloor x \rfloor$ denotes the greatest integer not greater than x.
-----Constraints-----
- $2 \leq N \leq 2\times 10^5$
- $|A_i|\leq 10^9$
- All values in input are integers.
-----Input-----
Input is given from Standard Input in the following format:
N
A_1 ... A_N
-----Output-----
Print the maximum possible sum of the chosen elements.
-----Sample Input-----
6
1 2 3 4 5 6
-----Sample Output-----
12
Choosing 2, 4, and 6 makes the sum 12, which is the maximum possible value.
输入格式
见题面
输出格式
见题面
样例输入
6
1 2 3 4 5 6
样例输出
12