sub BEGIN {
    ($_ = shift(@ARGV)) foreach (($B, $A, $p));
}
LINE: while (defined(($_ = <ARGV>))) {
    (/pat/ and ((@l = ()), do {
        <ARGV> foreach (1 .. $A)
    }, next));
    push(@l, $_);
    (($B < @l) and print(shift(@l)));
}
{
    print(@l);
}