s = eval(input())

for i in range(len(s)):

    for j in range(i+1,len(s)):

        if s[i] == s[j]:

            print('no')

            exit()

    

print('yes')
import sys

s = eval(input())

s = sorted(s)



for i in range(1,len(s)):

    if s[i] == s[i-1]:

        print('no')

        sys.exit()

print('yes')
s = eval(input())
for i in range(len(s)):
    for j in range(i + 1, len(s)):
        if s[i] == s[j]:
            print("no")
            exit()
print("yes")

import sys

s = eval(input())
s = sorted(s)
for i in range(1, len(s)):
    if s[i] == s[i - 1]:
        print("no")
        sys.exit()
print("yes")

+import sys + -for i in range(len(s)): -    for j in range(i + 1, len(s)): -        if s[i] == s[j]: -            print("no") -            exit() +s = sorted(s) +for i in range(1, len(s)): +    if s[i] == s[i - 1]: +        print("no") +        sys.exit()