# Given dictionaries, d1 and d2, create a new dictionary with the following
# property: for each entry (a, b) in d1, if there is an entry (b, c) in d2, then
# the entry (a, c) should be added to the new dictionary.  For example, if d1 is
# {2:3, 8:19, 6:4, 5:12} and d2 is {2:5, 4:3, 3:9}, then the new dictionary
# should be {2:9, 6:3} Associate the new dictionary with the variable d3

d3 = {}
for (k, v) in d1.iteritems():
  if v in d2:
    d3[k] = d2[v]