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"
    "os"
    "strconv"
    "strings"
    "fmt"
)

var sc = bufio.NewScanner(os.Stdin)

func main() {
    sc.Scan()
    lst := strings.Split(sc.Text(), " ")
    ab, _ := strconv.Atoi(lst[0])
    bc, _ := strconv.Atoi(lst[1])
    fmt.Println(ab * bc / 2)
}