#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
sys.setrecursionlimit(10**7)
from pprint import pprint as pp
from pprint import pformat as pf

import math
#from sortedcontainers import SortedList, SortedDict, SortedSet # no in atcoder
import bisect


if __name__ == '__main__':
    r = int(input())
    ans = 2 * r * math.pi
    print('ans') # debug
    print(ans)

    print('\33[32m' + 'end' + '\033[0m') # debug
