{
	my @next = (10, 1..9); # d -> next number not yet used ending with digit d
	my $carry = ""; # concatenation of first n terms minus n first digits
	sub nexta {
		if ($carry ne "") {
			my $d = substr($carry, 0, 1);
			my $a = $next[$d];
			$next[$d] += 10;
			$carry = substr($carry, 1) . $a;
			return $a;
		} else {
			my $a = -1;
			foreach my $next (@next) {
				if (substr($next,0,1) eq substr($next,-1)) {
					if ($a==-1 || $a > $next) {
						$a = $next;
					}
				}
			}
			$next[$a%10] += 10;
			$carry = substr($a, 1);
			return $a;
		}
	}
}

foreach my $n (1..10_000) {
	my $a = nexta();
	print "$n $a\n";
}