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

Example Input: SJIkEibGrqcrOBgGjYjJc, EervOGrqcrOBgGJZyx
Example Output: GrqcrOBgG

Example Input: oDdulHNcCdgbRGxiBTxM, kDcCdgbRGnsJlvas
Example Output: cCdgbRG

Example Input: cKBXWDsWcMyGRvDuuormyojQA, erhvLvyGRvDuuormVgLqh
Example Output:
yGRvDuuorm