var ic = 3;
var mainArray1 = new Array(ic);        
mainArray1[0] = 'images/main_01_a.jpg';
mainArray1[1] = 'images/main_02_a.jpg';
mainArray1[2] = 'images/main_03_a.jpg';

var mainArray2 = new Array(ic);  
mainArray2[0] = 'images/main_01_b.jpg';
mainArray2[1] = 'images/main_02_b.jpg';
mainArray2[2] = 'images/main_03_b.jpg';

var mainArray3 = new Array(ic);  
mainArray3[0] = 'images/main_01_c.jpg';
mainArray3[1] = 'images/main_02_c.jpg';
mainArray3[2] = 'images/main_03_c.jpg';

function pickRandom(range) {
	if (Math.random)
		return Math.round(Math.random() * (range-1));
	else {
		var now = new Date();
		return (now.getTime() / 1000) % range;
	}
}

var choice = pickRandom(ic);