Problem:
Score : 100 points

Problem Statement

There is a right triangle ABC with ∠ABC=90°.

Given the lengths of the three sides, |AB|,|BC| and |CA|, find the area of the right triangle ABC.

It is guaranteed that the area of the triangle ABC is an integer.

Constraints

1 \leq |AB|,|BC|,|CA| \leq 100

All values in input are integers.

The area of the triangle ABC is an integer.

Input

Input is given from Standard Input in the following format:

|AB| |BC| |CA|

Output

Print the area of the triangle ABC.

Sample Input 1

3 4 5

Sample Output 1

6

This triangle has an area of 6.

Sample Input 2

5 12 13

Sample Output 2

30

This triangle has an area of 30.

Sample Input 3

45 28 53

Sample Output 3

630

This triangle has an area of 630.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Web;
using System.IO;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Numerics;
using System.Diagnostics;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using static System.Math;
 

class P
{
    static void Main()
    {
        Console.WriteLine(Console.ReadLine().Split().Select(int.Parse).OrderBy(x => x).Take(2).Aggregate(1, (x, y) => x * y) / 2);
    }
}