var chapter_list = new Array(
  ["Vol.01 Ch.001","v01/c001"],
  ["Vol.01 Ch.002","v01/c002"],
  ["Vol.01 Ch.003.1","v01/c003.1"],
  ["Vol.01 Ch.003.2","v01/c003.2"],
  ["Vol.01 Ch.003.3","v01/c003.3"],
  ["Vol.01 Ch.003.4","v01/c003.4"],
  ["Vol.01 Ch.004.1","v01/c004.1"],
  ["Vol.01 Ch.004.2","v01/c004.2"],
  ["Vol.02 Ch.004.3","v02/c004.3"],
  ["Vol.02 Ch.005.1","v02/c005.1"],
  ["Vol.02 Ch.005.2","v02/c005.2"],
  ["Vol.02 Ch.005.3","v02/c005.3"],
  ["Vol.02 Ch.005.4","v02/c005.4"],
  ["Vol.02 Ch.005.5","v02/c005.5"],
  ["Vol.02 Ch.005.6","v02/c005.6"],
  ["Vol.02 Ch.005.7","v02/c005.7"],
  ["Vol.02 Ch.005.8","v02/c005.8"],
  ["Vol.02 Ch.006.1","v02/c006.1"],
  ["Vol.02 Ch.006.2","v02/c006.2"],
  ["Vol.02 Ch.006.3","v02/c006.3"],
  ["Vol.02 Ch.006.4","v02/c006.4"],
  ["Vol.02 Ch.006.5","v02/c006.5"],
  ["Vol.03 Ch.007.1","v03/c007.1"],
  ["Vol.03 Ch.007.2","v03/c007.2"],
  ["Vol.03 Ch.007.3","v03/c007.3"],
  ["Vol.03 Ch.008.1","v03/c008.1"],
  ["Vol.03 Ch.008.2","v03/c008.2"],
  ["Vol.03 Ch.008.3: extra","v03/c008.3"]
);

var total_chapters = 28;

for (var i = 0; i < chapter_list.length; i++) {
  document.getElementById('top_chapter_list').options[i] = new Option(chapter_list[i][0], chapter_list[i][1]);
  document.getElementById('bottom_chapter_list').options[i] = new Option(chapter_list[i][0], chapter_list[i][1]);
}
document.getElementById('top_chapter_list').value=current_chapter;
document.getElementById('bottom_chapter_list').value=current_chapter;
var current_chapter_index = document.getElementById('top_chapter_list').selectedIndex;