Crystal's fortune predict system is successfully developed!
The predict system is a distributed system consists of

computers. When it receives a predict request, each computer will generate one lowercase letter as its output. The final fortune predict result is determined by the concentration of all

outputs.
Tired of getting bad predictions like

, Ben decides to hack into the predict system and modify the predict result. He has already got the access permission of every computer in the predict system, so he can modify their output to any letter arbitrarily.
As Ben is going to take part in ICPC Asia Regional Kunming Site 2077, he wants predictions like

or

. He has found that the more times the substring

occurs in the concentration of all

outputs, the luckier he will get in the contest. But as the contest is coming soon, he only has time to modify at most

outputs of the computers in the predict system.
As Ben is busy hacking into the system, could you tell him how to get the most

substrings after his modification?