var chapter_list = new Array(
  ["Vol.01 Ch.000","v01/c000"],
  ["Vol.01 Ch.001","v01/c001"],
  ["Vol.01 Ch.002","v01/c002"],
  ["Vol.01 Ch.003","v01/c003"],
  ["Vol.01 Ch.003.5: Extra","v01/c003.5"],
  ["Vol.02 Ch.004","v02/c004"],
  ["Vol.02 Ch.005.1","v02/c005.1"],
  ["Vol.03 Ch.005.2","v03/c005.2"],
  ["Vol.03 Ch.006.1","v03/c006.1"],
  ["Vol.03 Ch.006.2","v03/c006.2"],
  ["Vol.04 Ch.007","v04/c007"],
  ["Vol.04 Ch.008","v04/c008"],
  ["Vol.04 Ch.009","v04/c009"],
  ["Vol.05 Ch.010","v05/c010"],
  ["Vol.05 Ch.011","v05/c011"],
  ["Vol.05 Ch.012","v05/c012"],
  ["Vol.06 Ch.013","v06/c013"],
  ["Vol.06 Ch.014","v06/c014"]
);

var total_chapters = 18;

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;