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 Python (3.4.3) (judge verdict: Accepted)

import collections
s = input()
alph = "abcdefghijklmnopqrstuvwxyz"
col = dict(collections.Counter(s))

flag = True
for i in range(26):
    if col.get(alph[i], 0) > 1:
        print("no")
        flag = False
        break
if flag:
    print("yes")