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 PHP7 (7.0.15) (judge verdict: Runtime Error)

<?php
# 文字列の入力
fscanf(STDIN, "%s", $s);

$len = str_len($s);

for($i=0;$i<$len;$i++){
  $count = substr_count ($s, substr($s,$i,1));
  if ($count > 1) {
    echo "no\n";
    exit;
  }
}
echo "yes\n";
?>