CF小白

（水题）

最简解法(之一）：

A. Domino piling

You are given a rectangular board of M × N squares. Also you are given an unlimited number of standard domino pieces of 2 × 1 squares. You are allowed to rotate the pieces. You are asked to place as many dominoes as possible on the board so as to meet the following conditions:

1. Each domino completely covers two squares.

2. No two dominoes overlap.

3. Each domino lies entirely inside the board. It is allowed to touch the edges of the board.

Find the maximum number of dominoes, which can be placed under these restrictions.

Input

In a single line you are given two integers M and N — board sizes in squares (1 ≤ M ≤ N ≤ 16).

Output

Output one number — the maximal number of dominoes, which can be placed.

Examples

input

2 4

output

4

input

3 3

output

4

 题目链接如下：

Problem - 50A - Codeforces

// Domino piling
#include<stdio.h>
int main(){int M,N;int re;scanf("%d%d",&M,&N);re=(M*N)/2;printf("%d",re);
}

主要从M，N的奇偶性，考虑：

任意一边为偶数和两边都是奇数，分为两类。

任意一边为偶数：一定能铺满；两边都是奇数时：一定会空出1*1 Square的空间。

最后发现转换为int时，奇数偶数情况一样。

居然真的AC掉了！