var chapter_list = new Array(
  ["Vol.01 Ch.000","v01/c000"],
  ["Vol.02 Ch.000","v02/c000"],
  ["Vol.03 Ch.000","v03/c000"],
  ["Vol.04 Ch.011: Devil's Mirror","v04/c011"],
  ["Vol.04 Ch.012: Spunk","v04/c012"],
  ["Vol.04 Ch.013: Halloween","v04/c013"],
  ["Vol.04 Ch.013.5: I'm Not A Gangster!!","v04/c013.5"],
  ["Vol.05 Ch.014","v05/c014"],
  ["Vol.05 Ch.015: Conflict","v05/c015"],
  ["Vol.05 Ch.016","v05/c016"],
  ["Vol.05 Ch.017","v05/c017"],
  ["Vol.05 Ch.018.1","v05/c018.1"],
  ["Vol.05 Ch.018.2: End","v05/c018.2"]
);

var total_chapters = 13;

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;