package Circle;

my $PI = 3.1415926;

sub new {
    my $class = shift;
    my ($radius) = @_;

    return bless {
        radius => $radius
    }, $class;
}

sub radius {
    my $self = shift;
    return $self->{radius};
}

sub area {
    my $self = shift;
    return $PI * $self->radius ** 2;
}

sub stretch {
    my $self = shift;
    my ($amount) = @_;

    $self->{radius} += $amount;

    return;
}