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



import sys

import subprocess

import json

import time

import math

import re

import sqlite3





S = eval(input())

dic = {}

for c in S:

    if c in dic:

        print("no")

        exit(0)

    dic[c] = 1

print("yes")



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



import sys

import subprocess

import json

import time

import math

import re

import sqlite3





S = eval(input())

if len(set(S)) == len(S): print("yes")

else: print("no")



# -*- coding: utf-8 -*-
import sys
import subprocess
import json
import time
import math
import re
import sqlite3

S = eval(input())
dic = {}
for c in S:
    if c in dic:
        print("no")
        exit(0)
    dic[c] = 1
print("yes")

# -*- coding: utf-8 -*-
import sys
import subprocess
import json
import time
import math
import re
import sqlite3

S = eval(input())
if len(set(S)) == len(S):
    print("yes")
else:
    print("no")

-dic = {} -for c in S: -    if c in dic: -        print("no") -        exit(0) -    dic[c] = 1 -print("yes") +if len(set(S)) == len(S): +    print("yes") +else: +    print("no")