function dropdownmenu(el)
{
    if (document.getElementById(el).style.visibility == 'visible')
    {
	    document.getElementById(el).style.display = 'none';
        document.getElementById(el).style.visibility = 'hidden';
    }
    else
    {
        document.getElementById(el).style.display = 'block';
        document.getElementById(el).style.visibility = 'visible';
    }
}