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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Main
{
    class Program
    {
        static void Main(string[] arg)
        {

            //string[] nm = Console.ReadLine().Split(' ');
            //int n = int.Parse(nm[0]);
            //int m = int.Parse(nm[1]);
            int[] line = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            Console.WriteLine(line[0] * line[1] * 0.5);
            //Console.ReadLine();

        }
    }
}