input: Write a function to compute the sum of the values of a given dictionary.
  dict_sum(dictionary):
      sum = 0
      for key, value in dictionary.items():
          sum += value
      return sum
  assert dict_sum({'A':5, 'B':6, 'C':10})==21
output: dict_sum(dictionary):
      sum = 0
      for key, value in dictionary.items():
          sum += value
      return sum