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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.IOException;

import java.io.BufferedReader;
import java.io.InputStreamReader;

import java.io.PrintWriter;

import java.util.TreeSet;

@SuppressWarnings("unchecked")
public class Main {
    public static void main(String[] args) throws IOException {
        final String s;

        try (
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(System.in))) {
            s = reader.readLine();
        }

        PrintWriter out = new PrintWriter(System.out);

        final String[] sl = s.split(" ");
        int AB = Integer.parseInt(sl[0]);
        int BC = Integer.parseInt(sl[1]);
        int CA = Integer.parseInt(sl[2]);

        TreeSet<Integer> ts = new TreeSet<>();
        ts.add(AB);
        ts.add(BC);
        ts.add(CA);

        int ans = 1;
        int cnt = 1;
        for (Integer i : ts) {
            if (2 < cnt) break;
            ans *= i;
            cnt++;
        }

        out.println(ans / 2);

        out.flush();
    }
}