# Replace the if/elsif block inside mce_loop with the following

   # Fill worksheet rows/cells
   if ($region eq 'AMS') {
      $wb = init_wb(0); $ws = $wb->sheets(0);
      $ws->write(0, 2, 'foo', $format);
      for my $row (1..1e6) { for my $cell (0..19) {
         $ws->write($row, $cell, $row + $cell + 10e6);
      }}
      print "AMS  ---- DONE.\n";
   }
   elsif ($region eq 'APJ') {
      $wb = init_wb(1); $ws = $wb->sheets(1);
      $ws->write(0, 2, 'bar', $format);
      for my $row (1..1e6) { for my $cell (0..19) {
         $ws->write($row, $cell, $row + $cell + 20e6);
      }}
      print "APJ  ---- DONE.\n";
   }
   elsif ($region eq 'EMEA') {
      $wb = init_wb(2); $ws = $wb->sheets(2);
      $ws->write(0, 2, 'baz', $format);
      for my $row (1..1e6) { for my $cell (0..19) {
         $ws->write($row, $cell, $row + $cell + 30e6);
      }}
      print "EMEA ---- DONE.\n";
   }