P15041 [UOI 2022 II Stage] Letter Ring

Ksenia is learning the English alphabet. She considers a string to be **alphabetical** if and only if all its letters are consecutive in the alphabet. For example, the strings **abc**, **xy**, **fg** are **alphabetical**, while **adef**, **zxc**, **zab** are not. Ksenia has a ring with letters written on it. She wants to find the longest **alphabetical** string on this ring and output its length. A string belongs to the ring if and only if all its characters are adjacent on the ring. In the ring, adjacent characters are the characters numbered $1$ and $2$, $2$ and $3$, $\ldots$, $n-1$ and $n$, and $n$ and $1$. For example, the string **abc** belongs to the ring **bcda**, while the string **bda** does not.

The first line contains an integer $n$ ($1 \leq n \leq 10^4$) — the length of the ring. The second line contains a lowercase Latin string of length $n$ — the letter ring.

Output one number — the length of the longest **alphabetical** string that belongs to the ring.

### Sample Explanation Explanation for the first test case: The string **abcd** satisfies the condition (indices 4, 1, 2, 3 are adjacent), and it is the longest. Explanation for the second test case: Among all **alphabetical** strings with only one letter, the string **a** is the smallest. Explanation for the third test case: Among all **alphabetical** strings, the string **mnop** is the longest. The full English alphabet in order is: **abcdefghijklmnopqrstuvwxyz**. ### Scoring If the longest **alphabetical** string belongs exactly to the input string (rather than the ring), then a solution that correctly handles this case will receive $60$ points. Translated by DeepSeek V3. Translated by ChatGPT 5