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

Example Input: UiaECWZf, gRyaECWLGRl
Example Output: aECW

Example Input: UmYbssMbmsXkKQuzNasLOib, EMqlbmsXkKQuzNcyHrpZXOQW
Example Output: bmsXkKQuzN

Example Input: ilgSzrcUKLTNLJbMKMKSt, hFXIuUKLTNLJbMKWxSCkDjY
Example Output:
UKLTNLJbMK