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)

// https://atcoder.jp/contests/abc116/tasks/abc116_a
// +build ignore

package main

import (
	"fmt"
	"sort"
)

func main() {
	var area int
	sides := make([]int, 3)
	for i := 0; i < 3; i++ {
		fmt.Scan(&sides[i])
	}
	sort.Sort(sort.IntSlice(sides))
	area = (sides[0] * sides[1]) / 2
	fmt.Println(area)
}