Problem:
Score : 100 points

Problem Statement

Print the circumference of a circle of radius R.

Constraints

1 \leq R \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

R

Output

Print the circumference of the circle.
Your output is considered correct if and only if its absolute or relative error from our answer is at most 10^{-2}.

Sample Input 1

1

Sample Output 1

6.28318530717958623200

Since we accept an absolute or relative error of at most 10^{-2}, 6.28 is also an acceptable output, but 6 is not.

Sample Input 2

73

Sample Output 2

458.67252742410977361942

Solution in Rust (1.42.0) (judge verdict: Accepted)

macro_rules! get_one {
    ($t:ty) => {{
        let mut line: String = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.trim().parse::<$t>().unwrap()
    }};

    ($t:ty; $n:expr) => {
        (0..$n).map(|_| get_one!($t)).collect::<Vec<_>>()
    };
}

use std::f64;

fn main() {
    let r = get_one!(i32);

    let l = 2. * (r as f64) * f64::consts::PI;
    println!("{}", l);
}