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

Example Input: GBTHKtWUzK, ovVNKtWUmVJF
Example Output: KtWU

Example Input: nOfXJySmVaJIindcJavXh, YpJWmVaJIindcJnoxyRvunG
Example Output: mVaJIindcJ

Example Input: JgjpQTRcarrJZ, jFkLnQTRcaWg
Example Output:
QTRca