function changeTab(tab) 
{
	if(tab == 'first') 
	{
		document.getElementById('first').setAttribute("class", "active first");
		document.getElementById('second').setAttribute("class", "");
		document.getElementById('third').setAttribute("class", "last");
		document.getElementById('first_content').setAttribute("class", "tab-cont");
		document.getElementById('second_content').setAttribute("class", "tab-cont hide");
		document.getElementById('third_content').setAttribute("class", "tab-cont hide");
	}
	if(tab == 'second') 
	{
		document.getElementById('first').setAttribute("class", "first");
		document.getElementById('second').setAttribute("class", "active");
		document.getElementById('third').setAttribute("class", "last");
		document.getElementById('first_content').setAttribute("class", "tab-cont hide");
		document.getElementById('second_content').setAttribute("class", "tab-cont");
		document.getElementById('third_content').setAttribute("class", "tab-cont hide");
	}
	if(tab == 'third') 
	{
		document.getElementById('first').setAttribute("class", "first");
		document.getElementById('second').setAttribute("class", "");
		document.getElementById('third').setAttribute("class", "active last");
		document.getElementById('first_content').setAttribute("class", "tab-cont hide");
		document.getElementById('second_content').setAttribute("class", "tab-cont hide");
		document.getElementById('third_content').setAttribute("class", "tab-cont");
	}

}