Fading pics

Okay, i have a movie with 20 pics, on 20 layers…every time one fades out you’d see the one bellow it…they’re sequential…this is the AS:


this.onEnterFrame = function() {
	if (pic1._alpha>0) {
		pic1._alpha -= 4;
	}
	if (pic1._alpha<=0) {
		pic2._alpha -= 4;
	}
	if (pic2._alpha<=0) {
		pic3._alpha -= 4;
	}
	if (pic3._alpha<=0) {
		pic4._alpha -= 4;
	}
	if (pic4._alpha<=0) {
		pic5._alpha -= 4;
	}
	if (pic5._alpha<=0) {
		pic6._alpha -= 4;
	}
	if (pic6._alpha<=0) {
		pic7._alpha -= 4;
	}
	if (pic7._alpha<=0) {
		pic8._alpha -= 4;
	}
	if (pic8._alpha<=0) {
		pic9._alpha -= 4;
	}
	if (pic9._alpha<=0) {
		pic10._alpha -= 4;
	}
	if (pic10._alpha<=0) {
		pic11._alpha -= 4;
	}
	if (pic11._alpha<=0) {
		pic12._alpha -= 4;
	}
	if (pic12._alpha<=0) {
		pic13._alpha -= 4;
	}
	if (pic13._alpha<=0) {
		pic14._alpha -= 4;
	}
	if (pic14._alpha<=0) {
		pic15._alpha -= 4;
	}
	if (pic15._alpha<=0) {
		pic16._alpha -= 4;
	}
	if (pic16._alpha<=0) {
		pic17._alpha -= 4;
	}
	if (pic17._alpha<=0) {
		pic18._alpha -= 4;
	}
	if (pic18._alpha<=0) {
		pic19._alpha -= 4;
	}
	if (pic19._alpha<=0) {
		pic20._alpha -= 4;
	}
};


it works perfectly until the 12th mc, then it just stops working, i can’t figure out why for the end of the world…i’ve tried several different ways, and it always stops working around the 12-13th mc…