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.*;
import java.util.*;

class Main {
  public static void main(String[] args) throws IOException{
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String[] strs = br.readLine().split(" ");
    int[] num = new int[3];
    for (int i = 0; i < 3; i++) {
      num[i] = Integer.parseInt(strs[i]);
    }
    Arrays.sort(num);
    
    System.out.println(num[0] * num[1] / 2);
  }
}