A13148 | $Domino for Young$

时间限制1s

内存限制256MB

通过 / 提交0/0

题目描述

You are given a Young diagram. Given diagram is a histogram with $n$ columns of lengths $a_1, a_2, \ldots, a_n$ ( $a_1 \geq a_2 \geq \ldots \geq a_n \geq 1$ ). ![](/uploads/acgo/image/21d56a150d865d94_cd411465af7c.jpeg)Young diagram for $a=[3,2,2,2,1]$ .Your goal is to find the largest number of non-overlapping dominos that you can draw inside of this histogram, a domino is a $1 \times 2$ or $2 \times 1$ rectangle.

The first line of input contain one integer $n$ ( $1 \leq n \leq 300\,000$ ): the number of columns in the given histogram. The next line of input contains $n$ integers $a_1, a_2, \ldots, a_n$ ( $1 \leq a_i \leq 300\,000, a_i \geq a_{i+1}$ ): the lengths of columns.

Output one integer: the largest number of non-overlapping dominos that you can draw inside of the given Young diagram.

输入 #1

5
3 2 2 2 1

输出 #1

C++ 编辑器

输入

输出