input: Write a function called `dict_sum` that takes a dictionary as an input and returns the sum of all the values in the dictionary.
  assert dict_sum({'A':5, 'B':6, 'C':10}) == 21
  assert dict_sum({'X':1, 'Y':2, 'Z':3}) == 6
  assert dict_sum({}) == 0
  assert dict_sum({'One':11, 'Two':22, 'Three':33}) == 66
output: def dict_sum(d):
      return sum(d.values())