use warnings;
use strict;
use feature "switch";

my $letter;
given ($ARGV[0]) {
    when ([0..39])   { $letter = 'F' ; }
    when ($_ <= 49)  { $letter = 'E' ; }
    when ($_ <= 59)  { $letter = 'D' ; }
    when ($_ <= 64)  { $letter = 'C' ; }
    when ($_ <= 69)  { $letter = 'C+'; }
    when ($_ <= 74)  { $letter = 'B' ; }
    when ($_ <= 79)  { $letter = 'B+'; }
    when ($_ <= 100) { $letter = 'A' ; }
}

if ($letter) {
    print "The student has gotten a $letter grade for the score of $ARGV[0].\n";
}
else {
    print "Please enter a value between 0 and 100\n"; 
}