CF 50A Domino piling

题目大概就是有个N*M的方块，然后有1*2面积的木板；

问在不重合的情况最多可以放多少块；

奇数偶数问题；

如果是偶数则一定能放下整数倍；

否则最多就是（奇数-1）的整数倍；

A. Domino piling

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

You are given a rectangular board of M × N squares. Also you are given an unlimited number of standard domino pieces of2 × 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 andN — 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

AC代码：

#include <bits/stdc++.h>
using namespace std ;
int main()
{
	int n , m ;
	cin>>n>>m;
	int sum;
	if(n*m%2==0)
	{
		sum=n*m/2;
	}
	else 
	{
		sum=(n*m-1)/2;
	}
	cout<<sum<<endl;
	return 0 ;
}