#!usr/bin/perl
use strict;
use warnings;
use List::Util qw(sum);

my @windsordigits;
while (my $x = <DATA>){
  next unless $x =~ /WINDSOR\sRIVERSIDE/;
  push @windsordigits, +(split /,/, $x)[-1];
}
die "No 'Windsor digits found in input\n" unless @windsordigits;
my $average = sum(@windsordigits) / @windsordigits;
print "Average is: $average\n";

__DATA__
CA006139520,"WINDSOR RIVERSIDE, ON CA",2018-01-02,10
CA006139520,"WINDSOR RIVERSIDE, ON CA",2018-01-02,20
CA006139520,"WINDSOR RIVERSIDE, ON CA",2018-01-02,14
CA006139520,"WINDSOR DRIVE, ON CA",2018-01-02,10