You are given a string S consisting of lowercase English letters. Determine whether all the characters in S are different.

-----Constraints-----
- 2 ≤ |S| ≤ 26, where |S| denotes the length of S.
- S consists of lowercase English letters.

-----Input-----
Input is given from Standard Input in the following format:
S

-----Output-----
If all the characters in S are different, print yes (case-sensitive); otherwise, print no.

-----Sample Input-----
uncopyrightable

-----Sample Output-----
yes

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