input: Write a python function to find the maximum occurring character in a given string.
  assert max_occurring_char("Python is an interesting language") == 'n'
  assert max_occurring_char("hello world") == 'l'
  assert max_occurring_char("aaaabbbcc") == 'a'
output: def max_occurring_char(s):
      from collections import Counter
      count = Counter(s)
      return max(count, key=count.get)