# Arup Guha
# 12/11/2024
# Solution to UCF HS Online Div 2 Problem: The Royal Wedding

import math

# Get input.
toks = input().split()
area = int(toks[0])
mult = int(toks[1])

# Do some math, shape is a circle.
# pi*r*r = A, so r= sqrt(A/pi) and circumference = 2pir = 2sqrt(piA)
circumference = 2*((math.pi*area)**.5)

# Print result, rounded as requested.
print("%.2f" % round(mult*circumference,2))