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::{stdin, stdout, StdinLock, StdoutLock, BufReader, BufWriter, BufRead, Write};

fn main() {
    let (std_in, std_out) = (stdin(), stdout());
    let mut io = IO::new(std_in.lock(), std_out.lock());
    let r = io.r::<f64>();
    io.w(2.0 * r * 3.1415926535);
}


struct IO<'a> {
    br: BufReader<StdinLock<'a>>,
    bw: BufWriter<StdoutLock<'a>>,
}

#[allow(dead_code)]
impl IO<'_> {
    fn new<'a>(il: StdinLock<'a>, ol: StdoutLock<'a>) -> IO<'a> {
        IO {br: BufReader::new(il), bw: BufWriter::new(ol) }
    }

    fn r<T: std::str::FromStr>(&mut self) -> T {
        let mut buf = String::new();
        self.br.read_line(&mut buf).ok();
        buf.trim().parse().ok().unwrap()
    }

    fn rb(&mut self) -> Vec<u8> {
        let mut buf = String::new();
        self.br.read_line(&mut buf).ok();
        buf.trim().as_bytes().to_vec()
    }

    fn rv<T: std::str::FromStr>(&mut self) -> Vec<T> {
        let mut buf = String::new();
        self.br.read_line(&mut buf).ok();
        buf.trim().split_whitespace().map(|e| e.parse().ok().unwrap()).collect()
    }

    fn rvb(&mut self) -> Vec<Vec<u8>> {
        let mut buf = String::new();
        self.br.read_line(&mut buf).ok();
        buf.trim().split_whitespace().map(|e| e.as_bytes().to_vec()).collect()
    }

    fn w<T: std::fmt::Display>(&mut self, x: T) {
        let _ = writeln!(self.bw, "{}", x);
    }

    fn wb(&mut self, s: &[u8]) {
        let _ = writeln!(self.bw, "{}", unsafe{std::str::from_utf8_unchecked(s)});
    }

    fn wv<T: std::fmt::Display>(&mut self, v: &[T]) {
        let _ = write!(self.bw, "{}", v[0].to_string());
        for x in v[1..].iter() {
            let _ = write!(self.bw, " {}", x.to_string());
        }
        let _ = writeln!(self.bw);
    }

    fn wvb(&mut self, v: &[Vec<u8>]) {
        let _ = write!(self.bw, "{}", unsafe{std::str::from_utf8_unchecked(&v[0])});
        for x in v[1..].iter() {
            let _ = write!(self.bw, " {}", unsafe{std::str::from_utf8_unchecked(x)});
        }
        let _ = writeln!(self.bw);
    }
}