A. A Substring
As is known to all, for any abc contest, its first problem (A) is always extremely easy.
For this problem, follow under steps:
- Scan the string, and check the pos i.
- If i=N-B (Last B chars), skip.
- Else, output current char.
Since N \le 20, this program can pass in <= 1ms.
(I think there is no need to provide the code.)