How to insert javascript method return values into sql server database

<asp:HiddenField ID="hdn_Lat" runat="server" Value="0" />
<asp:TextBox ID="txtAddress" runat="server" /> <br />
<asp:Button ID="btnAdd" runat="server" Text ="Add Location"
OnClientClick="javascript:return GetLocation();" onclick="btnAdd_Click1" />
<asp:Label ID="Label1" runat="server">


Javascript method:

<script type="text/javascript">
<!--
function GetLocation() {
var geocoder = new google.maps.Geocoder();
var address = document.getElementById("txtAddress").value;
var hdnLat = document.getElementById('<%= hdn_Lat.ClientID %>').value;
geocoder.geocode({ 'address': address }, function (results, status) {
if (status == google.maps.GeocoderStatus.OK) {
var latitude = results[0].geometry.location.lat();
var longitude = results[0].geometry.location.lng();
hdnLat = latitude;
alert(hdnLat);
//alert("Latitude: " + latitude + "\nLongitude: " + longitude);
} else {
alert("Request failed.")
}
});
};
//-->
</script>


Code behind:

protected void btnAdd_Click1(object sender, EventArgs e)
{

//string value ;
//ClientScript.RegisterStartupScript(this.GetType(), "GetData", "a=GetLocation():alert(a)", true);

Label1.Text = hdn_Lat.Value;

}