I debug and test my program for a day I can't find how's wrong.
So I want some test data to test my program. Thank you.

Maybe your program doesn't work correctly with such test cases when
the beginning of one word is the same as the ending of another  (or
itself). For example, here are a few cases with answers:
3 3 1
QWE
QQ
The answer is 22, but not 21 as your program might output. And, the
one for you to check your long mathematics:
50 8 2
QWERTYUI
QWERT
ERTYU
ETYUI
YUIE
The answer is 39215055148328

Hope this will help.
Good luck!

I think your input is incorrect. Please help me!