print "Enter a Roman numeral: ";
chomp ($_ = <STDIN>);

unless (m/^
        m{0,3}    # thousands
        (cm|dc{0,3}|cd|c{0,3})    # hundreds
        (xc|lx{0,3}|xl|x{0,3})    # tens
        (ix|vi{0,3}|iv|i{0,3})    # ones
        $/ix) {
  die "That doesn't appear to be a well-formed Roman numeral.\n";
}

$val = 0;
if (s/cm//i) {$val += 900;}
if (s/cd//i) {$val += 400;}
if (s/xc//i) {$val += 90;}
if (s/xl//i) {$val += 40;}
if (s/ix//i) {$val += 9;}
if (s/iv//i) {$val += 4;}
while (m/m/g) {$val += 1000;}
while (m/d/g) {$val += 500;}
while (m/c/g) {$val += 100;}
while (m/l/g) {$val += 50;}
while (m/x/g) {$val += 10;}
while (m/v/g) {$val += 5;}
while (m/i/g) {$val += 1;}

print "$val\n";
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