How to count records of table and bind to GridView in ASP.Net

This way

HTML:

<form id="form1" runat="server">
    <div>
        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
            <Columns>
                <asp:BoundField DataField="RollNo" HeaderText="RollNo" />
                <asp:BoundField DataField="Name" HeaderText="Name" />
                <asp:BoundField DataField="MsgTemplateName" HeaderText="Template Name" />
                <asp:BoundField DataField="SentMessagesCount" HeaderText="Sent Messages Count" />
            </Columns>
        </asp:GridView>
    </div>
    </form>

C#:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            this.PopulateGridView();
        }
    }

    private void PopulateGridView()
    {
        string constr = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
        using (SqlConnection conn = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT [RollNo], Name, [MsgTemplateName] ,COUNT(RollNo) AS SentMessagesCount FROM [Messages] GROUP BY [RollNo], Name, [MsgTemplateName]", conn))
            {
                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {

                    conn.Open();
                    DataSet ds = new DataSet();
                    da.Fill(ds);
                    GridView1.DataSource = ds;
                    GridView1.DataBind();
                    conn.Close();
                }
            }
        }
    }

NameSpace:

using System.Configuration;
using System.Data;
using System.Data.SqlClient;

Thank You.