codeforces50/A

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 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

Copy

2 4

output

Copy

4

input

Copy

3 3

output

Copy

4
题解：不难发现，如果总面积是奇数，则肯定有一块没法用，如果是偶数，总有办法铺满

#include<iostream>
#include<string>
#include<cstring>
using namespace std;
typedef long long ll;
int main()
{
    int m,n;
    cin>>m>>n;
    cout<<m*n/2;
    return 0;
 }