Kinda easy, though I still don't understand how I happened to make it work ("unless" and "and" priorities were fun to test) :D

sub f{
  $_="Adrien, Benjamin, Philippe";
  ${$_}=shift@_ for(m/\b(\w)/g);
  $B unless$P and f($B,$B+$A,$P><DATA>?$P-$.:$?,);
}
print f($|++,<DATA>,shift@ARGV),"\n";
__DATA__
1
[download]

run it with a numerical argument.

P!