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: Accepted)

# 英小文字からなる文字列 S が与えられます。
# S に含まれる文字がすべて異なるか判定してください。

s = gets.chomp

diff = true

s.length.times do |i|
  (s.length - i - 1).times do |j|
    if s[i + j + 1] == nil
      break
    end
    
    if s[i] == s[i + j + 1]
      diff = false
      break
    end
  end
  
  unless diff
    break
  end
end

if diff
  puts "yes"
else
  puts "no"
end