If the total number of substrings is less than k , print a string saying "No such line." (without the quotes).

翻译没有说明无解的情况，应加上

若 $k$ 大于子串的个数(无解)，输出No such line.

markdown:

若 $k$ 大于子串的个数(无解)，输出```No such line.`