import java.util.*;
public class MyClass {
static boolean contains_unique_chars(String s) {
char[] arr = s.toCharArray();
Arrays.sort(arr);
for (int i = 0; i < arr.length - 1; i++) {
if (arr[i] == arr[i + 1])
return false;
}
return true;
}
public static void main(String args[]) {
String s = "abcde";
if (contains_unique_chars(s)) {
System.out.println("yes");
}
else {
System.out.println("no");
}
}
}