input: Write a python function to calculate the floor, ceil, and pow2 of a given number.
  assert floor(4.7) == 4
  assert ceil(4.2) == 5
  assert pow2(3) == 8
output: import math
  
  def floor(x):
      return math.floor(x)
  
  def ceil(x):
      return math.ceil(x)
  
  def pow2(x):
      return 2 ** x