import java.util.Scanner;
public class Main{
public static void main(String[] args){
Scanner sc=new Scanner(System.in);
String str=sc.next();
int []cnt=new int[26];
for(char c:str.toCharArray())
cnt[c-‘a’]++;
for(char c:str.toCharArray()){
if(cnt[c-‘a’]==1){
System.out.println(c);
return ;
}
}
System.out.println(“no”);
}
}