import java.io.; import java.util.; import java.util.stream.*;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */

    try(Scanner s = new Scanner(System.in)){
        //System.out.println("Enter your string");
        String str = s.next();
        //System.out.println("Enter Sub String size or length");
         int len = s.nextInt();

      System.out.println(getSmallestAndLargest(str, len));

    }
}

public static String getSmallestAndLargest(final String str, final int l){
    if(Objects.isNull(str) || str.isBlank() || str.length()< l  || l<=0 || str.length()>1000){
        return "";
    }
   List<String> s = IntStream.range(0, str.length()-l+1)
    .mapToObj(i-> str.substring(i, i+l))
    .map(String::trim)
    .distinct()
    .sorted()
    .collect(Collectors.toList());

    if(s.size() >2){
       return String.format("%s"+"\n"+"%s", s.get(0), s.get(s.size()-1)); 
    }


    if(s.size() ==1){
       return String.format("%s"+"\n"+"%s", s.get(0), s.get(0)); 
    }

    return "";
}

}