my %from_to_bytes;
my %col_headings;

while (<DATA>) {
    ( $from, $to, $hh, $mm, $bytes ) = /^(\S+) (\S+) (\d+):(\d+) (\d+)$/
      or ( warn "bad format on line $.: $_" ), next;
    $from_to_bytes{$from}{$to} += $bytes;
    $from_to_bytes{$from}{"~~TOTAL"} += $bytes;
    $from_to_bytes{"~~TOTAL"}{$to} += $bytes;
    $col_headings{$to} = undef;
}