In this task, you are given two lists A,B. Find the longest common subsequence in the lists A and B.
[4515, 't', 9815, 1305, 'X', '817', '8739', 'F', '7197', 'y', 'C', 'C', 'w', 'W', 'B', '2121', 'M', 'W', 3943], ['S', 'f', 'b', 'b', 'X', '817', '8739', 'F', '7197', 'y', 'C', 'C', 'w', 'W', 'B', '2121', 'H', 's', 'c']