function showCurrentDiv(num)
{
    var divNum = document.getElementById('nav').getElementsByTagName('div');
	for (var i=0;i<divNum.length ;i++ )
	{   
	    if(typeof(divNum[i]) != "undefined"){
			divNum[i].style.display = 'none';
		}
	}
	if(typeof(divNum[num]) != "undefined"){
			divNum[num].style.display = 'block';
		}   
}