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: Runtime Error)

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Diagnostics;
class Program
{
    public static Scanner input;
    static void Main()
    {

        input = new Scanner();
        int first = input.Int();
        var arr = new List<double>();
        arr.Add(first);
        while(true)
        {
            if (arr.Count==0)
            {
                arr.Add(first);
            }
            else
            {
                arr.Add(f(arr[arr.Count-1]));
            }
            for(int a = 0; a < arr.Count-1; a++)
            {
                if (arr[a] == arr[arr.Count - 1]) { WriteLine(arr.Count - 1); break; }
            }
        }

    }
    static double f(double a)
    {
        if (a%2 == 0)
        {
            return (double)(a/2);
        }
        else
        {
            return (double)(3*a+1);
        }

    }
}

class Scanner
{

    public Scanner()
    {
    }

    public void skip()
    {
        ReadLine();
        return;
    }
    public string String()
    {
        return ReadLine();
    }
    public string[] arrayString()
    {
        return ReadLine().Split();
    }
    public int Int()
    {
        return int.Parse(ReadLine());
    }
    public int[] arrayInt()
    {
        return ReadLine().Split().Select(i => int.Parse(i)).ToArray();
    }
    public long Long()
    {
        return long.Parse(ReadLine());
    }
    public long[] arrayLong()
    {
        return ReadLine().Split().Select(i => long.Parse(i)).ToArray();
    }
    public double Double()
    {
        return double.Parse(ReadLine());
    }
    public double[] arrayDouble()
    {
        return ReadLine().Split().Select(i => double.Parse(i)).ToArray();
    }
}