There are some problems with mark and release.
Don't use mark and release, because the judge system will
give you wrong answer even though your program is correct,
this happens because mark and release are obsolete and
delphi doesn't correctly support them.
Also don't use assign(f, 'con'); if you want to test your
programs with files use assign(input, filename) and remove
it later.This way you can do regular read/readln's which
work correctly.Follow the same rule for output i.e. assign
(output, filename); .