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 (Python):
import bisect
import copy
import heapq
import sys
import itertools
import math
import queue
input = sys.stdin.readline
sys.setrecursionlimit(1000000)
mod = 10 ** 9 + 7

def read_values(): return map(int, input().split())
def read_index(): return map(lambda x: int(x) - 1, input().split())
def read_list(): return list(read_values())
def read_lists(N): return [read_list() for n in range(N)]
def init_dp1(init, N): return [init for _ in range(N)]
def init_dp2(init, N, M): return [[init for _ in range(M)] for _ in range(N)]


class V:
    def __init__(self, f, v=None):
        self.f = f
        self.v = v
 
    def __str__(self):
        return str(self.v)
 
    def ud(self, n):
        if n is None:
            return

        if self.v is None:
            self.v = n
            return
        self.v = self.f(self.v, n) 


def main():
    R = int(input())
    print(math.pi * 2 * R)


if __name__ == "__main__":
    main()

Solution (Python):
import math
r = int(input())
pi = math.pi
ans =r*2*pi

print(ans)

Solution (Python):
import numpy as np
n=int(input())
print(n*2*np.pi)

Solution (Python):
R = int(input())
print(3.1415926535*R*2)

Solution (Python):
R = int(input())
import math
print(2*R*math.pi)

Solution (Python):
R = int(input())
print(R * 2 * 3.141592)

Solution (Python):
import math
print(int(input())*2*math.pi)

Solution (Python):
import math
R = int(input())
print(2*R*math.pi)

Solution (Python):
import math

r = int(input())

print(2 * r * math.pi)

Solution (Python):
import math

r = int(input())
print(2*math.pi*r)

Solution (Python):
import math

i = int(input())

print(2 * math.pi * i)

Solution (Python):
import math

n = int(input())

print(2*n*math.pi)

Solution (Python):
def i1str():
    return input()


def istrs(n=None):
    if n is None:
        return input().split()
    a = []
    for _ in range(n):
        a.append(istrs())
    return a


def i1num():
    return int(input())


def inums(n=None):
    if n is None:
        return list(map(int, input().split()))
    a = []
    for _ in range(n):
        a.append(inums())
    return a


def ostrs(l, sp=" "):
    print(sp.join(l))


def onums(l, sp=" "):
    print(sp.join(map(str, l)))


def solve(n):
    pi = 3.14159
    return 2*pi*n


if __name__ == "__main__":
    n = i1num()
    print(solve(n))

Solution (Python):
import math

n = int(input())

print(math.pi * 2 * n)

Solution (Python):
import math
r = int(input())
print(2*r*math.pi)

Solution (Python):
import math
r=int(input())
print(math.pi*2*r)

Solution (Python):
import math

r = int(input())
print(2*r*math.pi)

Solution (Python):
from math import pi

r = int(input())

ans = 2 * r * pi
print(ans)

Solution (Python):
R = int(input())

print(2*3.141592*R)

Solution (Python):
import math
R = int(input())


print(2*math.pi*R)

Solution (Python):
import math

print(2 * math.pi * int(input()))

Solution (Python):
import math

R = int(input())
print(2 * math.pi * R)

Solution (Python):
r = int(input())
print(2*r*3.141592)

Solution (Python):
import math
R = int(input())
print(2 * R * math.pi)

Solution (Python):
from collections import deque
from heapq import heapify,heappop,heappush,heappushpop
from copy import copy,deepcopy
from itertools import permutations,combinations
from collections import defaultdict,Counter
from math import gcd,ceil,floor,factorial,pi

from functools import reduce
from pprint import pprint

def myinput():
    return map(int,input().split())

def mylistinput(n):
    return [ list(myinput()) for _ in range(n) ]

def mycol(data,col):
    return [ row[col] for row in data ]

def mysort(data,col):
    data.sort(key=lambda x:x[col],reverse=False)
    return data

def mymax(data):
    M = -1*float("inf")
    for i in range(len(data)):
        m = max(data[i])
        M = max(M,m)
    return M

def mymin(data):
    m = float("inf")
    for i in range(len(data)):
        M = min(data[i])
        m = min(m,M)
    return m

def myoutput(ls,space=True):
    if space:
        if len(ls)==0:
            print(" ")
        elif type(ls[0])==str:
            print(" ".join(ls))
        elif type(ls[0])==int:
            print(" ".join(map(str,ls)))
        else:
            print("Output Error")
    else:
        if len(ls)==0:
            print("")
        elif type(ls[0])==str:
            print("".join(ls))
        elif type(ls[0])==int:
            print("".join(map(str,ls)))
        else:
            print("Output Error")

import math
r = int(input())
ans = 2*pi*r
print(ans)

Solution (Python):
import math 
n=int(input())
cir = 2*math.pi*n
print(cir)

Solution (Python):
import math

print(2 * int(input()) * math.pi)

Solution (Python):
r = int(input())
import numpy as np
print(r * 2 * np.pi)

Solution (Python):
import sys
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
read = sys.stdin.buffer.read
sys.setrecursionlimit(10 ** 7)

import math

R = int(readline())
answer = 2 * R * math.pi
print(answer)

Solution (Python):
from math import pi

r = float(input())

print(2*r*pi)

Solution (Python):

r = int(input())
print(2*r*3.14159265)

Solution (Python):
print(int(input())* 2 * 3.1415)

Solution (Python):
from math import pi

R = int(input())
print(2 * pi * R)

Solution (Python):
import math

R = int(input())

print(math.pi * R * 2)

Solution (Python):
R = int(input())

print(2 * 3.1415926535 * R)

Solution (Python):
import math
R = int(input())
print(2 * R * math.pi)

Solution (Python):

import math
R = int(input())
print(2 * math.pi * R)

Solution (Python):
import numpy as np
R=int(input())
ans = R*2*np.pi
print(ans)

Solution (Python):

import math
R =int(input())
print(2*math.pi*R)

Solution (Python):
from math import pi
r = int(input())
print(2 * pi * r)

Solution (Python):
r = int(input())

p = 6.28318530717958623200

print(r*p)

Solution (Python):
from math import pi
print(int(input())*2*pi)

Solution (Python):
from collections import *
import sys
try: inp = raw_input
except: inp = input
def err(s):
    sys.stderr.write('{}\n'.format(s))

def ni():
    return int(inp())

def nl():
    return [int(_) for _ in inp().split()]

R = ni()
import math
print(math.pi*2*R)

Solution (Python):
import math
R = int(input())
print(2*R*math.pi)

Solution (Python):
import math
R = int(input())
print(R*2*math.pi)

Solution (Python):
import math
N = int(input())




print(2 * N * math.pi)

Solution (Python):
import math
print(2*(math.pi)*int(input()))

Solution (Python):

import math

R = int(input())
print(2*math.pi*R)

Solution (Python):
import math
R = int(input())
print(R*2*math.pi)

Solution (Python):
n = int(input())

print(n*2*3.1412)

Solution (Python):
import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians, gcd
from itertools import accumulate, permutations, combinations, product, groupby
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

R = INT()
print(2*R*pi)

Solution (Python):
from sys import stdin
from math import pi
input = stdin.readline

R = int(input())

print(2 * R * pi)

Solution (Python):
R = int(input())

print(2*R*3.14159)

Solution (Python):
import math
a = math.pi
r = int(input())
print(r * 2 * a)

Solution (Python):
r = int(input())
print(2*3.14159265*r)

Solution (Python):
N = int(input())
print(N * 6.283185307179586232)

Solution (Python):
import math
r = int(input())
r = r * 2 * math.pi
print(r)

Solution (Python):
r = int(input())
print(3.1415926535 * r * 2)

Solution (Python):
n = int(input())
print(n*6.28318530717958623200)

Solution (Python):
from math import pi

def main():
    print(int(input())*2*pi)
main()

Solution (Python):
import sys
input = sys.stdin.readline
import math
p = math.pi
R = int(input())
print(2*p*R)

Solution (Python):
r=int(input())
print(r*2*3.14)

Solution (Python):
r = int(input())
import math
print(2*math.pi*r)

Solution (Python):
import sys
from math import sqrt, pi
from collections import Counter, defaultdict, deque

input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)


def I():
    return int(input())


def MI():
    return map(int, input().split())


def LI():
    return list(MI())


def LIN(n: int):
    return [I() for _ in range(n)]


inf = float("inf")
mod = 10 ** 9 + 7


def main():
    r = I()
    print(2 * r * pi)
    pass


if __name__ == "__main__":
    main()

Solution (Python):
import math
n = int(input())
print(2 * math.pi * n)

Solution (Python):
r=int(input())
import math
print(2*math.pi*r)

Solution (Python):
from math import pi

R = int(input())
print(2 * R * pi)

Solution (Python):
import math
r = int(input())
ans = r*2*math.pi
print(ans)

Solution (Python):
import math
r = int(input())
print(2*r*math.pi)

Solution (Python):
import math
R = int(input())
print(2 * math.pi * R)

Solution (Python):
import math
R = int(input())
print(math.pi*2*R)

Solution (Python):
import math

print(2*int(input())*math.pi)

Solution (Python):
import math
r = int(input())
print(2 * r * math.pi)

Solution (Python):
import math
n = int(input())
print(2*n*math.pi)

Solution (Python):
import math
R = int(input())
print(math.pi * 2 * R)

Solution (Python):
pi = 6.28318530717958623200 / 2
print(pi * int(input()) * 2)

Solution (Python):
import math
R = int(input())
print(2*math.pi*R)

Solution (Python):
import math
R = int(input())

print(2*math.pi*R)

Solution (Python):
import math
r = int(input())
print(2*math.pi*r)

Solution (Python):
from math import pi
r = int(input())
print(2*r*pi)

Solution (Python):
pi = 3.14159265358979323846

R = int(input())
print(R*2*pi)

Solution (Python):
import math
print(math.pi * int(input()) * 2)

Solution (Python):
r=int(input())
print(2*3.1415926535*r)

Solution (Python):
R = int(input())
print(2*R*3.1415926535)

Solution (Python):
import math
s = int(input())
print(2*s*math.pi)

Solution (Python):
import math

R = int(input())

print(math.pi*2*R)

Solution (Python):
import math
r = int(input())
print(2*math.pi*r)

Solution (Python):
R = int(input())
res = R*3.141592*2
print(res)

Solution (Python):
import math
r=int(input())
print(2*r*math.pi)

Solution (Python):
import math
print(int(input())*math.pi*2)

Solution (Python):
r=int(input())
import math
print(r*2*math.pi)

Solution (Python):


import math

def main():
    r = int(input())

    print(2*r*math.pi)

if __name__ == '__main__':
    main()

Solution (Python):
r = int(input())
print(2*r*3.1416)

Solution (Python):
R = int(input())
print(R * 2 * 3.14)

Solution (Python):
import math
print(math.pi*int(input())*2)

Solution (Python):
R = int(input())
print(2*R*3.14159265358)

Solution (Python):
a=int(input())
print(2*3.1415926538*a)

Solution (Python):
r = int(input())
print(2*r*3.1415926)

Solution (Python):
R = int(input())
import math
p = math.pi
print(2*p*R)

Solution (Python):
pi = 3.141592653
r = int(input())
print(2 * pi * r)

Solution (Python):
import math

r = int(input())

print(2*r*math.pi)

Solution (Python):
import math
print(int(input())*2*math.pi)

Solution (Python):
import math
r = int(input())
print(2 * r * math.pi)

Solution (Python):
import sys
sys.setrecursionlimit(10000000)
import numpy as np


def main():
    R = int(input())
    print(np.pi * 2 * R)


if __name__ == '__main__':
    main()

Solution (Python):
import math
N = int(input())
print(2*math.pi*N)

Solution (Python):
import math
r = input()

print(math.pi * 2.0 * float(r))

Solution (Python):
import sys
input = sys.stdin.readline
sys.setrecursionlimit(int(1E+7))
pi = 3.141592653589793238
r = int(input())
print (2*pi*r)

Solution (Python):
a=float(input())
z=a*2*3.1415
print(z)

Solution (Python):
import math
R = int(input())
print(R* 2 * math.pi)

Solution (Python):
import math
n = int(input())
print(2*n*math.pi)

Solution (Python):
import sys
import os
from io import BytesIO, IOBase






'''def sieve(n):
    if n < 2: return list()
    prime = [True for _ in range(n + 1)]
    p = 3
    while p * p <= n:
        if prime[p]:
            for i in range(p * p, n + 1, p):
                prime[i] = False
        p += 2
    r = [2]
    for p in range(3, n + 1, 2):
        if prime[p]:
            r.append(p)
    return r'''


'''def divs(n, start=1):
    divisors = []
    for i in range(start, int(n**.5) + 1):
        if n % i == 0:
            if n / i == i:
                divisors.append(i)
            else:
                divisors.extend([i, n // i])
    return len(divisors)'''


'''def divn(n, primes):
    divs_number = 1
    for i in primes:
        if n == 1:
            return divs_number
        t = 1
        while n % i == 0:
            t += 1
            n //= i
        divs_number *= t
    return divs_number'''


'''def flin(d, x, default=-1):
    left = right = -1
    for i in range(len(d)):
        if d[i] == x:
            if left == -1: left = i
            right = i
    if left == -1:
        return (default, default)
    else:
        return (left, right)'''


'''def xor1_n(n):
    d={0:n,1:1,2:n+1,3:0}
    return d[n&3]'''

def cel(n, k): return n // k + (n % k != 0)
def ii(): return int(input())
def mi(): return map(int, input().split())
def li(): return list(map(int, input().split()))
def lcm(a, b): return abs(a * b) // math.gcd(a, b)
def prr(a, sep=' '): print(sep.join(map(str, a)))
def dd(): return defaultdict(int)
def ddl(): return defaultdict(list)
def ddd(): return defaultdict(defaultdict(int))


 
BUFSIZE = 8192
 
 
class FastIO(IOBase):
	newlines = 0
 
	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = "x" in file.mode or "r" not in file.mode
		self.write = self.buffer.write if self.writable else None
 
	def read(self):
			while True:
					b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
					if not b:
							break
					ptr = self.buffer.tell()
					self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
			self.newlines = 0
			return self.buffer.read()
 
	def readline(self):
			while self.newlines == 0:
					b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
					self.newlines = b.count(b"\n") + (not b)
					ptr = self.buffer.tell()
					self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
			self.newlines -= 1
			return self.buffer.readline()
 
	def flush(self):
			if self.writable:
					os.write(self._fd, self.buffer.getvalue())
					self.buffer.truncate(0), self.buffer.seek(0)
 
 
class IOWrapper(IOBase):
	def __init__(self, file):
			self.buffer = FastIO(file)
			self.flush = self.buffer.flush
			self.writable = self.buffer.writable
			self.write = lambda s: self.buffer.write(s.encode("ascii"))
			self.read = lambda: self.buffer.read().decode("ascii")
			self.readline = lambda: self.buffer.readline().decode("ascii")
 

sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

from collections import defaultdict 


from math import gcd,pi















r=ii()
print(2*pi*r)

Solution (Python):

import math
r = int(input())

print(2 * r * math.pi)

Solution (Python):
import sys
sys.setrecursionlimit(10**8)
def ii(): return int(sys.stdin.readline())
def mi(): return map(int, sys.stdin.readline().split())
def li(): return list(map(int, sys.stdin.readline().split()))
def li2(N): return [list(map(int, sys.stdin.readline().split())) for i in range(N)]
def dp2(ini, i, j): return [[ini]*i for i2 in range(j)]
def dp3(ini, i, j, k): return [[[ini]*i for i2 in range(j)] for i3 in range(k)]



import math
N = ii()

print(math.pi*2*N)

Solution (Python):
import math
r = int(input())
print(2 * r * math.pi)

Solution (Python):
import math

R = int(input())

print(2 * math.pi * R)

Solution (Python):
import math
R, = [int(x) for x in input().split()]
print(2 * math.pi * R)

Solution (Python):
import math

R = int(input())

pi = math.pi
print(2*R*pi)

Solution (Python):
import math
r = int(input())
print(2 * math.pi * r)

Solution (Python):
r = int(input())
pi = 6.28318530717958623200
print(r*pi)

Solution (Python):
from math import pi
R = int(input())
ans = pi * 2 * R
print(ans)

Solution (Python):
n = int(input())
print(n*6.28318530717958623200)

Solution (Python):
import math
r = int(input())
r = 2*r*math.pi
print(r)

Solution (Python):
import math
R = int(input())
print(2*math.pi*R)

Solution (Python):
import math

R=int(input())
print(math.pi*R*2)

Solution (Python):
import math
N = int(input())

print(2*N*math.pi)

Solution (Python):
import math

n = int(input())

print(2*n*math.pi)

Solution (Python):
import math
x = math.pi
y = int(input())
print (2*x*y)

Solution (Python):
import math
n = int(input())
print(2*n*math.pi)

Solution (Python):
r = int(input())
print(r * 2 * 3.14159265358979)

Solution (Python):
n = int(input())
import math





print(2*n*math.pi)

Solution (Python):

import numpy as np

def main():
    r = int(input())
    print(r * 2 * np.pi)

if __name__ == '__main__':
    main()

Solution (Python):
r = int(input())
import math
print(2*r*math.pi)

Solution (Python):
import math
r = int(input())



print(math.pi*2*r)

Solution (Python):
n=int(input())
print(n*2*3.1415926)

Solution (Python):
si = lambda: input().strip()
ii = lambda: int(input())
mii = lambda: map(int, input().split())
lmii = lambda: list(map(int, input().split()))
smii = lambda: sorted(map(int, input().split()))



from math import pi

R = ii()

print(R*2*pi)

Solution (Python):
from sys import stdin
from sys import setrecursionlimit
from math import pi
setrecursionlimit(10 ** 7)

n = int(stdin.readline().rstrip())

print(2*pi*n)

Solution (Python):
r = int(input())
print(2*r*3.141592)

Solution (Python):

import math
r = int(input())
print(2*math.pi * r)

Solution (Python):
from math import pi

R = int(input())
print(2 * R * pi)

Solution (Python):
import math 
r=int(input())
ans = 2*math.pi*r
print(ans)

Solution (Python):

import math
r = int(input())
print(2 * r * math.pi)

Solution (Python):
import math


r = int(input())
ans = 2* r * math.pi

print (ans)

Solution (Python):
import math
r=int(input())
print(math.pi * 2*r)

Solution (Python):
import math
N = int(input())
print(N * 2 * math.pi)

Solution (Python):
from math import pi
print(int(input())*2*pi)

Solution (Python):
import math
R=int(input())
print(2*R*math.pi)

Solution (Python):
import sys
import os
from io import BytesIO, IOBase






'''def sieve(n):
    if n < 2: return list()
    prime = [True for _ in range(n + 1)]
    p = 3
    while p * p <= n:
        if prime[p]:
            for i in range(p * p, n + 1, p):
                prime[i] = False
        p += 2
    r = [2]
    for p in range(3, n + 1, 2):
        if prime[p]:
            r.append(p)
    return r'''


'''def divs(n, start=1):
    divisors = []
    for i in range(start, int(n**.5) + 1):
        if n % i == 0:
            if n / i == i:
                divisors.append(i)
            else:
                divisors.extend([i, n // i])
    return len(divisors)'''


'''def divn(n, primes):
    divs_number = 1
    for i in primes:
        if n == 1:
            return divs_number
        t = 1
        while n % i == 0:
            t += 1
            n //= i
        divs_number *= t
    return divs_number'''


'''def flin(d, x, default=-1):
    left = right = -1
    for i in range(len(d)):
        if d[i] == x:
            if left == -1: left = i
            right = i
    if left == -1:
        return (default, default)
    else:
        return (left, right)'''


'''def xor1_n(n):
    d={0:n,1:1,2:n+1,3:0}
    return d[n&3]'''

def cel(n, k): return n // k + (n % k != 0)
def ii(): return int(input())
def mi(): return map(int, input().split())
def li(): return list(map(int, input().split()))
def lcm(a, b): return abs(a * b) // math.gcd(a, b)
def prr(a, sep=' '): print(sep.join(map(str, a)))
def dd(): return defaultdict(int)
def ddl(): return defaultdict(list)
def ddd(): return defaultdict(defaultdict(int))



BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
            while True:
                    b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
                    if not b:
                            break
                    ptr = self.buffer.tell()
                    self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
            self.newlines = 0
            return self.buffer.read()

    def readline(self):
            while self.newlines == 0:
                    b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
                    self.newlines = b.count(b"\n") + (not b)
                    ptr = self.buffer.tell()
                    self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
            self.newlines -= 1
            return self.buffer.readline()

    def flush(self):
            if self.writable:
                    os.write(self._fd, self.buffer.getvalue())
                    self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
            self.buffer = FastIO(file)
            self.flush = self.buffer.flush
            self.writable = self.buffer.writable
            self.write = lambda s: self.buffer.write(s.encode("ascii"))
            self.read = lambda: self.buffer.read().decode("ascii")
            self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

from collections import defaultdict 


from math import gcd,pi















r=ii()
print(2*pi*r)

Solution (Python):
from math import pi
r = int(input())
print(2*pi*r)

Solution (Python):
import math
r = int(input())
ans = 2 * r * math.pi
print(ans)

Solution (Python):
import math
r=int(input())
print(2*math.pi*r)

Solution (Python):
import math
r = int(input())

x = math.pi

ans = r*x*2
print(ans)

Solution (Python):











import sys
sys.setrecursionlimit(10**6)
input=sys.stdin.readline
from math import floor,sqrt,factorial,hypot,log,pi 
from heapq import heappop, heappush, heappushpop
from collections import Counter,defaultdict,deque
from itertools import accumulate,permutations,combinations,product,combinations_with_replacement
from bisect import bisect_left,bisect_right
from copy import deepcopy
from fractions import gcd
from random import randint
def ceil(a,b): return (a+b-1)//b
inf=float('inf')
mod = 10**9+7
def pprint(*A): 
    for a in A:     print(*a,sep='\n')
def INT_(n): return int(n)-1
def MI(): return map(int,input().split())
def MF(): return map(float, input().split())
def MI_(): return map(INT_,input().split())
def LI(): return list(MI())
def LI_(): return [int(x) - 1 for x in input().split()]
def LF(): return list(MF())
def LIN(n:int): return [I() for _ in range(n)]
def LLIN(n: int): return [LI() for _ in range(n)]
def LLIN_(n: int): return [LI_() for _ in range(n)]
def LLI(): return [list(map(int, l.split() )) for l in input()]
def I(): return int(input())
def F(): return float(input())
def ST(): return input().replace('\n', '')
def main():
    R=I()
    print(pi*R*2)
if __name__ == '__main__':
    main()

Solution (Python):
import math
R = int(input())
ans = 2 * R * math.pi
print(ans)

Solution (Python):

from math import pi
r=int(input())
print(2*pi*r)

Solution (Python):





import math

r = int(input())
print(2 * math.pi * r)

Solution (Python):

import sys
input = sys.stdin.readline
import math

r = int(input())
print(r * 2.0 * math.pi)

Solution (Python):
r = int(input())

print(r * 2 * 3.14)

Solution (Python):
import math


R = int(input())


print(R*2*math.pi)

Solution (Python):
import math

R = int(input())
print(2 * R * math.pi)

Solution (Python):
import math
a=math.pi
s=int(input())
b=2*a*s
print(b)

Solution (Python):
from math import pi
a = int(input())


print(2*pi*a)

Solution (Python):
r=int(input())
pi=3.14159
print(2*pi*r)

Solution (Python):
import math

r = int(input())
ans = math.pi*(2*r)
print(ans)

Solution (Python):
import sys, re, os
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import permutations, combinations, product, accumulate
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from heapq import heapify, heappop, heappush

def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def S_MAP(): return map(str, input().split())
def LIST(): return list(map(int, input().split()))
def S_LIST(): return list(map(str, input().split()))
 
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

R = INT()
print(R * 2 * pi)

Solution (Python):
import math
print (2*int(input())*math.pi)

Solution (Python):
import math

r = int(input())
print(2*r*math.pi)

Solution (Python):
import sys
sys.setrecursionlimit(10**8)
def ii(): return int(sys.stdin.readline())
def mi(): return map(int, sys.stdin.readline().split())
def li(): return list(map(int, sys.stdin.readline().split()))
def li2(N): return [list(map(int, sys.stdin.readline().split())) for i in range(N)]
def dp2(ini, i, j): return [[ini]*i for i2 in range(j)]
def dp3(ini, i, j, k): return [[[ini]*i for i2 in range(j)] for i3 in range(k)]



import math
N = ii()

print(math.pi*2*N)

Solution (Python):
R = int(input())
import math
print(2*R*math.pi)

Solution (Python):
from sys import stdin
import math
n = int(stdin.readline().rstrip())
print(2*n*math.pi)

Solution (Python):
import numpy as np


def main():
    R = int(input())
    print(2 * R * np.pi)


if __name__ == '__main__':
    main()

Solution (Python):
from sys import stdin
from sys import setrecursionlimit
from math import pi
setrecursionlimit(10 ** 7)

n = int(stdin.readline().rstrip())

print(2*pi*n)

Solution (Python):
import math
pi = math.pi
r = int(input())
print(2 * r * pi)

Solution (Python):
import math

R = int(input())

print(R*2*math.pi)

Solution (Python):
import math
r=int(input())
print(2*r*math.pi)

Solution (Python):
import math
R = int(input())
print(2*math.pi*R)

Solution (Python):
import math

r = int(input())
print(2*r*math.pi)

Solution (Python):
import math
R = int(input())
print(2*math.pi*R)

Solution (Python):
import numpy as np
R = int(input())
print(2*np.pi*R)

Solution (Python):
import math as m
r = int(input())
print(2*m.pi*r)

Solution (Python):
n = int(input())
print(2*n*3.14159265)

Solution (Python):
import math
n = int(input())
print(2*math.pi*n)

Solution (Python):
r = int(input())
import math

print( 2 * r * math.pi)

Solution (Python):
import math

r = int(input())

print(2 * r * math.pi)

Solution (Python):
import math
print(2*math.pi*int(input()))

Solution (Python):
import numpy as np
R = int(input())
print(np.pi * 2 * R)

Solution (Python):
import math
r = int(input())
print(2*r*math.pi)

Solution (Python):
import math

r = int(input())

print(2*r*math.pi)

Solution (Python):
R = int(input())
import math
print(R*2*math.pi)

Solution (Python):
import sys
import math

sys.setrecursionlimit(10 ** 7)
f_inf = float('inf')
mod = 10 ** 9 + 7


def resolve():
    r = int(input())
    print(2 * r * math.pi)


if __name__ == '__main__':
    resolve()

Solution (Python):

hankei = int(input())
print(2 * 3.1415 * hankei)

Solution (Python):

import math
math.pi
N = int(input())
print(N*math.pi*2)

Solution (Python):
r = int(input())
print(2*r*3.14)

Solution (Python):
import sys
from math import pi
r = int(sys.stdin.readline().rstrip())
def main():
    print(r * 2 * pi)

if __name__ == '__main__':
    main()

Solution (Python):
import math

r = int(input())

print(2 * r * math.pi)

Solution (Python):
import math
r = int(input())

print(2*math.pi*r)

Solution (Python):
from math import pi

r = int(input())

print(2 * pi * r)

Solution (Python):
import math

R = int(input())
print(2*math.pi*R)

Solution (Python):
a=int(input())
print(a * 2* 3.1415)

Solution (Python):
r = int(input())
print(3.1415926535*2*r)

Solution (Python):
from collections import deque, Counter as cnt
from collections import defaultdict as dd
from operator import itemgetter as ig
from bisect import bisect_right as bsr
from math import factorial, ceil, floor
import sys
sys.setrecursionlimit(1000000)


args = None
INF = float("inf")
MOD = int(1e9 + 7)


def input(*ps):
    if type(ps[0]) is list:
        return [input(*ps[0][:-1]) for _ in range(ps[0][-1])]
    elif len(ps) == 1:
        return ps[0](next(args))
    else:
        return [p(next(args)) for p in ps]


def nlist(n, v):
    if not n:
        return [] if type(v) is list else v
    return [nlist(n[1:], v) for _ in range(n[0])]


def yesno(v):
    print(["Yes", "No"][not v])



def main():
    R = input(int)
    print(R * 2 * 3.14)


if __name__ == '__main__':
    args = iter(sys.stdin.read().split())
    main()

Solution (Python):
R = int(input())

print(3.141592*2*R)

Solution (Python):
from sys import stdin
import math


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    R = int(_in[0])  
    
    cnt = 2*math.pi*R
    
    print(cnt)

Solution (Python):
import math

n = int(input())
print(math.pi*2*n)

Solution (Python):
from heapq import heappush, heappop
from itertools import permutations, accumulate, combinations
import math
import bisect
import numpy as np
from collections import defaultdict, deque
from operator import itemgetter
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)




def main():
    n = int(input())
    pi = math.pi
    print(2 * n * pi)


if __name__ == '__main__':
    main()

Solution (Python):
import math
print(int(input())*2*math.pi)

Solution (Python):
import math
r = int(input())

print(2*math.pi*r)

Solution (Python):
import math


r = int(input())
print(r*2*math.pi)

Solution (Python):
import math

R = int(input())

print(2 * math.pi * R)

Solution (Python):
r = int(input())
puy = 3.141592
print(2* puy * r)

Solution (Python):
import math

n = int(input())
print(2*n*math.pi)

Solution (Python):
print(int(input())*2*3.14)

Solution (Python):
import math 
N=int(input())
print(2*N*math.pi)

Solution (Python):
import math
def main():
    R = int(input())
    return(R*2*math.pi)

print(main())

Solution (Python):
import math
r = int(input())
print(2*math.pi*r)

Solution (Python):
import math
R = int(input())
print(math.pi*2*R)

Solution (Python):
def main():
    import sys
    input = sys.stdin.readline
    print(int(input())*3.141592653589*2)

if __name__ == '__main__':
    main()

Solution (Python):
print(2*(22/7)*int(input()))