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)

use std::io;
use std::f32::consts::PI;

fn main() {
    let n: f32 = read::<f32>();

    println!("{}", n * 2.0 * PI);
}

fn read<T: std::str::FromStr>() -> T {
    let mut line = String::new();
    io::stdin().read_line(&mut line).ok();
    line.trim().parse().ok().unwrap()
}