var chapter_list = new Array(
  ["Vol.01 Ch.001: Black Airs Appear!","v01/c001"],
  ["Vol.01 Ch.002: Monster Rebellion!","v01/c002"],
  ["Vol.01 Ch.003: Strenght Can Change Your Way of Thinking!","v01/c003"],
  ["Vol.01 Ch.004: The Complete Volume of Monsters & Adorable Monsters Which Got Scrapped","v01/c004"],
  ["Vol.02 Ch.001: The Helta Race","v02/c001"],
  ["Vol.02 Ch.002: Hell District One","v02/c002"],
  ["Vol.02 Ch.003: Gentle Weapon","v02/c003"],
  ["Vol.02 Ch.004: Soul","v02/c004"],
  ["Vol.02 Ch.005: Art Hall","v02/c005"]
);

var total_chapters = 9;

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;