'''You are provided with the radius of a circle "A". Find the length of its circumference.

Note: In case the output is coming in decimal, roundoff to 2nd decimal place. In case the input is a negative number, print "Error".

Input Description:
The Radius of a circle is provided as the input of the program.

Output Description:
Calculate and print the Circumference of the circle corresponding to the input radius up to two decimal places.

Sample Input :
2
Sample Output :
12.57'''
radius = float(input())
if radius > 0:
  circumference = (2 * 22 * radius)/7
  print(round(circumference,2))
else:
  print("Error")
