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 (1.15.1) (judge verdict: Accepted)

use std::io::stdin;

fn main() {
    let stdin = stdin();
    let mut buf = String::new();
    stdin.read_line(&mut buf).unwrap();
    let buf: Vec<i32> = buf.split_whitespace().map(|n| n.parse().unwrap()).collect();
    
    let ab = buf[0];
    let bc = buf[1];
    let ca = buf[2];
    
    let s = (ab + bc + ca) / 2;
    let S = ((s * (s - ab) * (s - bc) * (s - ca)) as f64).sqrt() as i32;
    
    println!("{}", S);
}