'''input
no
yes

uncopyrightable
yes

different
no

'''

# -*- coding: utf-8 -*-

# AtCoder Beginner Contest
# Problem B

if __name__ == '__main__':
    s = input()
    set_s = set(s)

    if len(s) == len(set_s):
        print('yes')
    else:
        print('no')

'''input
no
yes

uncopyrightable
yes

different
no

'''

# -*- coding: utf-8 -*-

# AtCoder Beginner Contest
# Problem B

if __name__ == '__main__':
    s = input()
    set_s = set(s)

    if len(s) == len(set_s):
        print('yes')
    else:
        print('no')

input
 no
 yes
 
 uncopyrightable
 yes
 
 different
 no # -*- coding: utf-8 -*- # AtCoder Beginner Contest # Problem B