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;

namespace AtCoder.ABC116
{
    public class A
    {
        public static void Solve()
        {
            string[] input = Console.ReadLine().Split(' ');
            int a = int.Parse(input[0]);
            int b = int.Parse(input[1]);
            
            
            Console.WriteLine((a * b) / 2);
        }    
    }
}

namespace AtCoder {
    class Program
    {
        static void Main(string[] args)
        {
            ABC116.A.Solve();
        }
    }
}