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.Linq;

namespace myApp
{
    public class Reader
    {
        //
        public int Int()
        {
            return int.Parse(Console.ReadLine());
        }

        //
        public int[] IntArray(char separator = ' ')
        {
            return Console.ReadLine().Split(' ').Select(v => int.Parse(v)).ToArray();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Reader reader = new Reader();

            int[] abc = reader.IntArray();

            Console.WriteLine((abc[0] * abc[1]) / 2);
        }
    }
}