use strict;
use warnings;

my %grade_lookup = (
   90 => "A", 
   80 => "B", 
   70 => "C", 
   60 => "D", 
);

my $score = <STDIN>;
chomp($score);

my $grade = "F";
foreach my $gate_score (sort { $a <=> $b } keys %grade_lookup) {
   if ( $score >= $gate_score ) {
      $grade = $grade_lookup{$gate_score};
   }
}

print("$score is $grade\n");

##</code><code>##

use strict;
use warnings;

my @grade_lookup = reverse(
   [ 90 => "A" ], 
   [ 80 => "B" ], 
   [ 70 => "C" ], 
   [ 60 => "D" ], 
);

my $score = <STDIN>;
chomp($score);

my $grade = "F";
foreach (@grade_lookup) {
   if ( $score >= $_->[0] ) {
      $grade = $_->[1];
   }
}

print("$score is $grade\n");