In the interactive tasks to print end-of-line in the end of the printed string (query or answer) and flush the output buffer (fflush(stdout) or cout.flush() in C/C++).
Your solutions are running under Linux, so take into account that any compiler-dependent features that work, for ex., under MSVC, may not work under the different OS and compiler.
If some important clarifications come, the pdf file with the statements and in-task statements (F5 needed to refresh sometime) are updated, so it may be useful to reload it in case of the global clars.
To check actual limitations (Time Limit, Memory Limit, Source Limit etc) use Summary tab.
You may download all samples and attachements from the contest tasks using Sample ZIP tab.