State of CheckBoxes While Paging in a GridView Control

protected void GridView1_PreRender(object sender, EventArgs e)
 {

     if (Session["page" + GridView1.PageIndex] != null)
     {
         int count = Convert.ToInt32(ViewState["total"]);
         CheckBox chb;
         bool[] values = (bool[])Session["page" + GridView1.PageIndex];

         for (int i = 0; i < GridView1.Rows.Count; i++)
         {
             chb = (CheckBox)GridView1.Rows[i].FindControl("chkStatus");

             chb.Checked = values[i];

         }

     }
 }

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{


Response.Write(GridView1.PageIndex.ToString());
int d = GridView1.PageCount;
bool[] values = new bool[GridView1.PageSize];

CheckBox chb;
int count = Convert.ToInt32(ViewState["total"]);
for (int i = 0; i < GridView1.Rows.Count; i++)
{
chb = (CheckBox)GridView1.Rows[i].FindControl("chkStatus");

if (chb != null)
{
values[i] = chb.Checked;
count++;
}
}
Session["page" + GridView1.PageIndex] = values;





GridView1.PageIndex = e.NewPageIndex;
DataTable dtPagination = ((DataTable)Session["details"]);
DataView dvPagination = new DataView(dtPagination);
GridView1.DataSource = dtPagination;
GridView1.DataBind();

}


i have use these two events i can check the checkbox in the paging but i want to know how many check boxes i have checked overall gridview with paging control.....