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 "fmt"
import "sort"

func main(){
    var a, b, c int

    fmt.Scan(&a)
    fmt.Scan(&b)
    fmt.Scan(&c)

    nums := []int{a, b, c}
    sort.Sort(sort.IntSlice(nums))

    fmt.Printf("%d\n", nums[0]*nums[1]/2)
}