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 PyPy3 (2.4.0) (judge verdict: Accepted)

S = input()

word = 'qwertyuiopasdfghjklzxcvbnm'

for i in range(len(word)):
    if S.count(word[i]) > 1:
        print('no')
        exit()
        
print('yes')