print nearest_power_of_2( 50 );
sub nearest_power_of_2 {
    my $x = shift;
    my $n = log( $x ) / log( 2 );
    return $x if $n == int $n;

    my ($below, $above) = (int $n, int $n + 1);
    $_ = 2 ** $_ for ($above, $below);
    return $above - $x > $x - $below ? $below : $above;
}