In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

Example Input: JXnHYuZvAYK, zhUYuZvASGhd
Example Output: YuZvA

Example Input: BICndZkjoSidWivWATvtqsS, FzVWjoSidWivFaQhkRT
Example Output: joSidWiv

Example Input: AkYuNemHGBEDF, uluNemHGAycbWX
Example Output:
uNemHG