function count(id)
{
	var counter;
	counter = document.getElementById('checkbox_counter').value;
			
	if ( document.getElementById(id).checked == true )
	{ 
		counter = counter*1 + 1;
	}
	else
	{
		counter = counter*1 - 1;
	}
			
	if (counter > 3)
	{
		alert( 'Prašome pasirinkti ne daugiau 3 užpildų' );
		document.getElementById(id).checked = false;
		counter = counter*1 - 1;
	}
	
	document.getElementById('checkbox_counter').value = counter;
}