P16994 [NWERC 2018] Kleptography

John likes simple ciphers. He had been using the “Caesar” cipher to encrypt his diary until recently, when he learned a hard lesson about its strength by catching his sister Mary browsing through the diary without any problems. Rapidly searching for an alternative, John found the famous “Autokey” cipher. He uses a version that takes the $26$ lower-case letters `a`--`z` and internally translates them in alphabetical order to the numbers $0$ to $25$. The encryption key $k$ begins with a secret prefix of $n$ letters. Each of the remaining letters of the key is copied from the letters of the plaintext $a$, so that $k_{n+i}=a_i$ for $i\ge 1$. Encryption of the plaintext $a$ to the ciphertext $b$ follows the formula $b_i=a_i+k_i \bmod 26$. Mary was able to get a peek at the last $n$ letters John typed before he noticed her, encrypted the text document, and left. This could be her chance.

The input consists of: - One line with two integers $n$ and $m$ ($1\le n\le 30$, $n+1\le m\le 100$), where $n$ is the keyword length as well as the number of letters Mary saw, and $m$ is the length of the text. - One line with $n$ lower-case letters, the last $n$ letters of the plaintext. - One line with $m$ lower-case letters, the whole ciphertext.

Output the plaintext of John's diary.