Sample data will be taken from `./sample/'.  All pairs of matching
(.in, .ans) files there will be used as sample data, in alphabetical
order by file name.  This data will be displayed in the problem
statement.

Secret test data will be taken from `./secret/'. All pairs of matching
(.in, .ans) files there will be used to test each
submission. Optionally a text file (with filename extension .txt)
describing the purpose of an input file may be present. For each .txt
file there must be a matching (.in,.ans) pair.
