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 Lua (5.3.2) (judge verdict: Accepted)

S = io.read()
set = {}
bool = false
for i = 1, #S do
    seq = string.sub(S, i, i)
    if set[seq] then
        bool = true
        break
    end
    set[seq] = true
end
print(bool and "no" or "yes")