Date to rotate objects?

I created a script that will rotate a different ad every day, based on a comparison of the current date & the ads assigned day. The bug in the script is that the number of ads vs the number of days may be odd, so the last one or two ads will miss a (days) rotation every month. Is there a way I can get this to work so every ad hits its rotation.

var displayAdOne:Array=new Array;

var displayAdTwo:Array=new Array;

var displayAdThree:Array=new Array;

var displayAdFour:Array=new Array;

var showAd:Loader = new Loader();

displayAdOne=[adOne, 1, 5, 9, 13, 17, 21, 25, 29];

displayAdTwo=[adTwo, 2, 6, 10, 14, 18, 22, 26, 30];

displayAdThree=[adThree, 3, 7, 11, 15, 19, 23, 27, 31];

displayAdFour=[adFour, 4, 8, 12, 16, 20, 24, 28];

var loopit = displayAdOne.length + displayAdTwo.length + displayAdThree.length + displayAdFour.length

//trace(loopit)

var theDate:Date = new Date;

var triggerDate=theDate.getDate();

trace(triggerDate)

for (var i=1; i<=9; i++)

{

if (triggerDate==displayAdOne)

{

showAd.load(adOne);

break;

}

if (triggerDate==displayAdTwo)

{

showAd.load(adTwo);

break;

}

if (triggerDate==displayAdThree)

{

showAd.load(adThree);

break;

}

if (triggerDate==displayAdThree)

{

showAd.load(adFour);

break;

}

addChild(showAd);

}

Thanks for any help given!