var current_main = 1;
function swapMain(number, cleartimeout)
{
	document.getElementById('main_' + number + '_content').style.display = 'block';
	document.getElementById('main_' + current_main + '_content').style.display = 'none';	
	current_main = number;
	if(cleartimeout == true)
	{
		clearInterval(timeout);
	}
}

function swapNextMain()
{
	if(current_main == 4)
	{
		swapMain(1);
	} else {
		swapMain(current_main + 1);	
	}
}

var timeout = setInterval(swapNextMain,5000);