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 OCaml (4.02.3) (judge verdict: Wrong Answer)

Scanf.scanf "%s" (fun s ->
    let n = String.length s in
    let rec loop i acc =
        if i = n then "yes" else
            let c = int_of_char s.[i] - 97 in
            let m = 1 lsl c in
            if m land acc = 0 then loop (i + 1) (acc lor c)
            else "no"
    in
    loop 0 0 |> print_endline
)