#!/usr/bin/perl

use warnings;
use strict;

my $string = "HEY I WANT TO YELL EVERYTHING. MY MOTHER DID NOT pay ME ENOUGH ATTENETION";

$string = join '. ',map {ucfirst} (split(/\. /,lc($string)));
$string =~ s/\bi\b/I/g;
$string .= '.';

print $string;