function chkData(f)
{

	if(f.txtName.value=="")
	{
			alert("Please enter your name.");
			f.txtName.focus();
			return false;
	}
		
	var em_check=echeck(f.txtEmail.value);
	if(em_check!=true )
	{
			alert(em_check);
			f.txtEmail.focus();
			return false;
	}
	if(f.txtHow.value=="")
	{
		alert("Please enter How did you know about us?.");
		f.txtHow.focus();
		return false;
	}
	if(f.txtComments.value=="")
	{
			alert("Please enter your Enquiry.");
			f.txtComments.focus();
			return false;
	}
}
// check the validity of email  
function echeck(str)
{
	var at="@";
	var dot=".";
	var lat=str.indexOf(at)
	var lstr=str.length
	var ldot=str.indexOf(dot)
	if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr-1)
	{
		return("Invalid E-mail ID")
	}
	if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr-1)
	{
		return("Invalid E-mail ID")
	}
	if (str.indexOf(at,(lat+1))!=-1)
	{
	    return ("Invalid E-mail ID")
	}
	if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot)
	{
		return ("Invalid E-mail ID")
	}
	if (str.indexOf(dot,(lat+2))==-1)
	{
		return ("Invalid E-mail ID")
	}
	if (str.indexOf(" ")!=-1)
	{
		return ("Invalid E-mail ID")
	}
	 return true					
}