import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class solution {
    static ArrayList<String> subList = new ArrayList<>();

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int k = sc.nextInt();
        System.out.println(subAllList(s, k));
    }

    private static String subAllList(String s, int k) {
        for (int i = 0; i <= s.length() - k; i++) {
            String stringList = s.substring(i, i + k);
            subList.add(stringList);
        }
        Collections.sort(subList);
        String smallest = subList.get(0);
        String largest = subList.get(subList.size() - 1);
        if (smallest.equalsIgnoreCase(largest)) {
            return smallest;
        } else {
            return smallest + "\n" + largest;
        }
    }
}