use Data::Dumper;
use strict;

my $hash = {};

my @files = ( "LOG1", "LOG2", "LOG3" );

foreach my $file ( @files ) {
  open FILE, "<", $file or die "Unable to open $file\n$!\n";
   
  my ( $date, $id, $timestamp ) = qw( Unknown "" "" );
  while (<FILE>) {
     chomp;
     if (/^\d/){ 
        $date = $_;
     } elsif (/^\s+ID\s*=\s*(.*)$/) {
        $id = $1;   
     } elsif ( /^\s+TIMESTAMP\s*=\s*(.*)$/ ) {
        $timestamp = $1;
     } elsif ( /^\s+COUNT_\d+\s*=\s*(.*)$/ ) {
        $hash->{$date}->{$id}->{$timestamp} += $1;
     }
  }
}

print Dumper($hash), "\n";