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

Example Input: QvtDqzQiSknPbRCG, hVxHdqzQiSknPbumdpNIf
Example Output: qzQiSknPb

Example Input: sbQJFbUtmnKaEJePFPeRM, QzfvkdZbUtmnKaEJNrWD
Example Output: bUtmnKaEJ

Example Input: KuAfeJcK, DSVJAfeJCi
Example Output:
AfeJ