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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"strings"

	"os"
	"sort"
	"strconv"
)

//scanで一行づつ読み込む
var sc = bufio.NewScanner(os.Stdin)
var wtr = bufio.NewWriter(os.Stdout)

//sort
// array := []int{5, 1, 4, 2, 3}
// sort.Sort(sort.IntSlice(array))

func main() {
	// a := make([]int, n)
	n := nextLine()
	n2 := strings.Split(n, " ")
	arr := []int{}
	for _, i := range n2 {
		j, _ := strconv.Atoi(i)
		arr = append(arr, j)
	}
	sort.Sort(sort.IntSlice(arr))
	a, b := arr[0], arr[1]

	fmt.Fprintln(wtr, (a*b)/2)
	_ = wtr.Flush()
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}