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1669. Universal Word

Time limit: 3.0 second
Memory limit: 64 MB
Now you are asked for help by the organizers of the Winter Olympic Games 2014, which, as you know, will be held in Yekaterinozavodsk. And although there are still 6 years ahead, the first sport facility is already put into operation. It is the track for the skiing race.
It was decided to construct a huge screen near the tribunes, which would show the name of a current leader during the race. It is known, that only the first N letters of English alphabet are used to write the names of the sportsmen, and each of the N letters should appear in each name exactly once. Technically, the screen looks like a word with letters from the English alphabet; each of these letters can either shine or stay dark. The organizers call the word “universal” if the screen based on it can display any possible name of a sportsman (possibly with some holes between neighboring letters). The governor proposed some word for the screen. You should tell whether this word is universal.

Input

The first line contains an integer N (1 ≤ N ≤ 26). The second line contains a word to check, consisting of lowercase English letters. The word can contain only first N letters of the alphabet. The length of the word doesn't exceed 300.

Output

Output “YES”, if the word, proposed by governor, is universal and “NO” otherwise.

Samples

inputoutput
3
abacaba
YES
3
abcba
NO
Problem Author: Ivan Burmistrov (prepared by Alex Samsonov)
Problem Source: Ural SU Contest. Petrozavodsk Winter Session, January 2008