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 PHP (7.4.4) (judge verdict: Accepted)

<?php

    // AtCoder Beginner Contest 163
    // A - Circle Pond

    $r = in_int();
    out($r * 2 * pi());

    // -----------------------------------------------------
    function in() { return trim(fgets(STDIN)); }
    function in_int() { return (int)in(); }
    function in_vals() { return explode(' ', in()); }
    function in_ints() { return array_map('intval', in_vals()); }
    function out($s) { echo $s . PHP_EOL; }
    function yes() { out('Yes'); }
    function no() { out('No'); }