def combine_dict(d1,d2):
if not d1:
return d2
elif not d2:
return d1
else:
for key in d2:
if key not in d1:
d1[key] = 0
d1[key] += d2[key]
return dict(sorted(d1.items()))
d1 = {'a': 1, 'b': 2}
d2 = {'c': 3, 'b': 4}
print(combine_dict(d1,d2))
ZGVmIGNvbWJpbmVfZGljdChkMSxkMik6CglpZiBub3QgZDE6CgkJcmV0dXJuIGQyCgllbGlmIG5vdCBkMjoKCQlyZXR1cm4gZDEKCWVsc2U6CgkJZm9yIGtleSBpbiBkMjoKCQkJaWYga2V5IG5vdCBpbiBkMToKCQkJCWQxW2tleV0gPSAwCgkJCWQxW2tleV0gKz0gZDJba2V5XQoJCXJldHVybiBkaWN0KHNvcnRlZChkMS5pdGVtcygpKSkKZDEgPSB7J2EnOiAxLCAnYic6IDJ9CmQyID0geydjJzogMywgJ2InOiA0fQpwcmludChjb21iaW5lX2RpY3QoZDEsZDIpKQoK