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::{self, Read, Write};

#[rustfmt::skip] #[macro_use] #[allow(unused_macros)]
mod rwc {
    macro_rules! rd { ($buf:ident, $t:ty)       => { $buf.next().unwrap().parse::<$t>().ok().unwrap() }; }
    macro_rules! wt { ($out:ident, $($arg:tt)*) => { write!($out, $($arg)*).ok()                      }; }
    macro_rules! cv { ($n:expr, $fn:expr)       => { (0..$n).map($fn).collect::<Vec<_>>()             }; }
}

fn main() {
    let (mut _buf, mut _out) = (String::new(), io::stdout());
    let (mut _buf, mut _out) = {
        io::stdin().read_to_string(&mut _buf).ok();
        (_buf.split_whitespace(), io::BufWriter::new(_out.lock()))
    };

    let r = rd!(_buf, f64);
    wt!(_out, "{:.10}\n", 2.0 * 3.1415 * r);
}