Distinct Substrings in Lexicographical Order

You are given a string s and an integer n. Your task is to extract all distinct contiguous substrings of length n from s and then output them in lexicographical order.

If n is greater than the length of s, output None. Otherwise, list all unique substrings of length n, sorted in lexicographical (dictionary) order. The output should be a single line containing the substrings separated by a single space.

Note: A substring is a contiguous sequence of characters within a string.

inputFormat

The input consists of two lines. The first line contains the string s (which does not contain spaces). The second line contains a positive integer n.

outputFormat

Output a single line with all distinct substrings of length n from s in lexicographical order separated by a space. If no substring of length n can be formed (i.e. if n is greater than the length of s), output None.

abcdef
3

abc bcd cde def