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 Ruby (2.3.3) (judge verdict: Wrong Answer)

s = gets.chomp
f = true
i = 0
s.chars{
  |ch|
  tmp = s
  tmp.slice!(i)
  puts "D:" + ch
  if tmp.index(ch) != nil then
    puts "no"
    exit
  end
  i += 1
}
puts "yes"