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 Rust (1.42.0) (judge verdict: Wrong Answer)

use proconio::input;

fn main (){

let mut _ab : i128;
let mut _bc : i128;
let mut _ca : i128;

input! {
    ab : i128,
    bc : i128,
    ca : i128,

}

let ans : i128 = (bc/2)*ab ; 
let ans_1 : i128 = ((bc+1)/2)*ab ; 

if bc % 2  == 0 {
    println!("{}",ans);
}else {
println!("{}",ans_1);
}
}