Oracle Devu and Longest Common Subsequence

Devu is a disastrous oracle: his predictions about various events of your life are horrifying. Instead of providing good luck, he "blesses" you with bad luck. The secret behind his wickedness is a hidden omen which is a string of length m. On your visit to him, you can ask a lot of questions about your future, each of which should be a string of length m. In total you asked him n such questions, d