use 5.012;
use List::Util qw[reduce];

sub str2num {
    my ($str, $base) = @_;
    reduce { $a * $base + $b } 0, split //, $str;
}

sub num2str {
    my ($num, $base) = @_;
    if ($num > 0) {
        num2str(int($num / $base), $base) . ($num % $base);
    }
    else {
    	'0';
    }
}