#!/usr/bin/env perl

use strict;
use warnings;

my %MWs;

#create the hash MWs with the amino acids and their molecular weight.

%MWs = (
    "A" => 71.1,    "D" => 115.0,    "F" => 146.1,    "H" => 137.1,
    "K" => 128.1,   "M" => 131.1,    "P" => 97.1,     "R" => 156.1,
    "T" => 101.1,   "W" => 186.2,    "C" => 103.1,    "E" => 129.1,
    "G" => 57.1,    "I" => 113.1,    "L" => 113.1,    "N" => 114.1,
    "Q" => 128.1,   "S" => 87.1,     "V" => 99.1,     "Y" => 163.1,
);

my $sum = 0.0;

print "Type amino acids. Hit [ctrl]-D when done.\n";

while ( my $line = <STDIN> ){
    chomp $line;
    next unless length $line;
    $sum += $MWs{$_} foreach
        grep {exists $MWs{$_}}
        map  {uc}
        split //, $line;
}

print "Molecular weight of this peptide is: $sum \n"