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 Julia (0.5.0) (judge verdict: Accepted)

const lines=readlines(open("/dev/fd/0"))
let
    state=0
    global input
    input()=lines[state+=1]
end
int(s::String)=parse(Int32,s)
intSub(s::SubString{String})=parse(Int32,s)
intLine()=map(intSub,split(input()))
function main()
    a,b,_=sort(intLine())
    print(Int(a*b/2))
end
main()