#! perl -slw
use strict;

### Prefer Ones:
### Write n zeros.
### Then, always write a one unless it would cause the repetition of an n-length string;
### In which case, write a zero.

our $N //= 4;

my $seq = '0' x $N;
my %seen = ( $seq => 1 );
for( $N .. 2**$N ) {
    $seq .= ( not exists $seen{ substr( $seq, -( $N-1 ) ) . '1' } ) ? '1' : '0';
    ++$seen{ substr( $seq, -$N ) };
}

$seq .= substr $seq, 0, $N-1;

print length $seq; <STDIN>;

my $re = '(.)(?=(' . '.'x($N-1) . '))';
print $1 . $2 while $seq =~ m[$re]g;


##</code><code>##

#! perl -slw
use strict;

### Prefer Ones:
### Write n zeros.
### Then, always write a one unless it would cause the repetition of an n-length string;
### In which case, write a zero.

our $N //= 4;

my $t1 = "b${ \(2**$N+$N-1) }";
my $seen = '';
my $mask1 = ( 1<<$N )-1;
my $seq = pack 'Q*', (0) x 100;
my $val = 0;

for( $N .. 2**$N+$N-1 ) {                   ## if N=5; 5 .. 36; if N=6, 6 .. 64+6-1 = 69;
    $val = ( $val << 1 ) & $mask1;
    vec( $seen, $val | 1, 1 ) or do{ $val |= 1; vec( $seq, $_, 1 ) = 1; };
    vec( $seen, $val    , 1 ) = 1;
}
print unpack $t1, $seq;