Problem 3¶ Write a Python function to combine two dictionary by adding values for common keys.¶ 1 2 3 4d1 = {'a': 100, 'b': 200, 'c':300} d2 = {'a': 300, 'b': 200, 'd':400} Output: Counter({'a': 400, 'b': 400, 'd': 400, 'c': 300})