function random_main_block(){
var myrandom = new Array()
myrandom[1]="block"
myrandom[2]="none"
myrandom[3]="block"
myrandom[4]="none"
myrandom[5]="block"
myrandom[6]="none"

var ra = Math.floor(Math.random()*myrandom.length)
if (ra == 0)
	ra = 1
	var a = document.getElementById("main_random_block_1_1");
	a.style.display = myrandom[ra];
	display_other_block();
}

function display_other_block(){
var a = document.getElementById("main_random_block_1_1");
var b = document.getElementById("main_random_block_1_2");
var c = document.getElementById("main_random_block_2_1");
var d = document.getElementById("main_random_block_2_2");
if(a){
	if(a.style.display == "block")
		{b.style.display = "none";
		c.style.display = "block";
		d.style.display = "none";}
	else{b.style.display = "block";
		c.style.display = "none";
		d.style.display = "block";};
	}
}