text: n = int(raw_input())
  nums = map(int, raw_input().split())
  wheights = map(int, raw_input().split())
  
  def m_sum(nums):
  	return reduce(lambda x,y: x + y, nums)
  
  def wheighted_mean(nums, n):
  	def wheighted_sum(x, y):
  		if type(x) == tuple:
  			return (x[0] * x[1]) + (y[0] * y[1])
  		else:
  			return x + (y[0] * y[1])
  	
  	m_wheighted_sum = reduce(wheighted_sum, zip(nums, wheights))
  	return  float(m_wheighted_sum) / float(m_sum(wheights))
  
  print "{0:.1f}".format(round(wheighted_mean(nums, wheights), 1)) 
  