var imagesList = [
'main_01.gif',
'main_02.gif',
'main_03.gif',
'main_04.gif',
'main_05.gif',
'main_06.gif',
'main_07.gif',
'main_08.gif',
'main_09.gif',
'main_10.gif',
'main_11.gif',
'main_12.gif',
'main_13.gif',
'main_14.gif',
'main_15.gif',
'main_16.gif',
'main_17.gif',
'main_18.gif',
'main_19.gif',
'main_20.gif'
];

 var aImages = [];
 for (var i = 0, len = imagesList.length; i < len; i++) {
        aImages[i] = new Image();
        aImages[i].src = 'images/'+imagesList[i];
 }