Problem:
Score : 200 points

Problem Statement

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 1

uncopyrightable

Sample Output 1

yes

Sample Input 2

different

Sample Output 2

no

Sample Input 3

no

Sample Output 3

yes

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.List

main = do
  s <- getLine
  putStr . f . sort $ s

f [x] = "yes"
f (x:y:zs) 
  | x == y = "no"
  | otherwise = f (y:zs)