use strict;
use warnings;

use feature 'say';
use List::Util 'min';

my @strs = (
    '0' x 1_000_000,
    '01' x 1_000_000,
    '011' x 1_000_000,
    '0110' x 1_000_000,
);

for (@strs) {
    my $l = length(tr/01//sr);
    my $d = length() - $l;
    say $l + min( $d, 2 );
}