<reponame>FGtatsuro/myatcoder<filename>beginner_contest/163/A.py
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

r = int(input())

import math

print(2 * r * math.pi)

import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

r = int(input())

import math

print(2 * r * math.pi)