use strict;
use warnings;

my $planet_count = "9";

while (1) {
    print "How many planets are there? ";
    chomp(my $planet_guess = <>);

    if ($planet_guess ne $planet_count) {
        print "Sorry that's not right, try again.\n";
        next;
    }
    else {
        print "Well done! There are indeed $planet_count planets in the solar system.\n";
        last;
    }
}