K. 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 a solution: 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 \(i \geq 1\). Encryption of the plaintext \(a\) to the ciphertext \(b\) follows the formula \(b_i = a_i + k_i \bmod 26\).

Mary is not easily discouraged. She was able to get a peek at the last \(n\) letters John typed into his diary on the family computer before he noticed her, quickly encrypted the text document with a click, 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 length of the keyword 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.

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출처 ICPC NWERC 2018