Varietas delectat 2

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class Varietasdelectat2 {


    public static void main(String[] args) throws IOException {

        BufferedReader br =new  BufferedReader(new InputStreamReader(System.in));

        String line;
        String[] st;
        Boolean flag = false;
        while ( !"0".equals(line= br.readLine())) {

            st = line.split(" ");
            flag = false;

            for ( int i = 1; i < st.length ; i++)
                for ( int j = i; j < st.length-1; j++)
                    if ( Integer.parseInt(st[i]) == Integer.parseInt(st[j+1]))
                        flag = true;

            if ( flag ) System.out.println("no");
            else System.out.println("yes");

        }

    }

}