my @range;
if( $cmonth > 2 ){
    @range = ($cmonth-2 .. $cmonth);
}
else{
    my $start = 10 + $cmonth;
    my $mid   = $start == 11 ? 12 : 1;
    @range = ($start,$mid,$cmonth);
}

if( grep{ $_ == $monthnr }@range ){
    print "...";
}