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 Scala (2.11.7) (judge verdict: Accepted)

object Main extends App {
    val s = io.StdIn.readLine

    def rec(str: String): Boolean = {
        if (str.length == 1) true
        else if (str.tail.contains(str.head)) false
        else rec(str.tail)
    }

    val result = rec(s)
    if (result) println("yes") else println("no")
}