public class Solution {
    public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";
                
        smallest = s.substring(0, k);
        largest = s.substring(0, k);
        
        for (int i = 1; i <= s.length() - k; i++) {
            String substring = s.substring(i, i + k);
            
            if (substring.compareTo(smallest) < 0) {
                smallest = substring;
            }
            if (substring.compareTo(largest) > 0) {
                largest = substring;
            }
        }
        
        return smallest + "\n" + largest;
}