#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1201251

use strict;
use warnings;

print "K sum";

for my $K ( 0..5 )
  {
  my $sum = 0;
  $sum += ($_ // 0) for (split ' ', "5 6 7 8\n")[0 .. $K-1];
  print "$K $sum";
  }
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Try yours with strict and warnings and see what you get