Get Count checked CheckBox in GridView in ASP.Net

This way:

<form id="form1" runat="server">
    <div>
        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
            <Columns>
                <asp:TemplateField HeaderText="ID">
                    <ItemTemplate>
                        <asp:CheckBox ID="chkId" runat="server" Text='<%# Eval("Id") %>' />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField DataField="Name" HeaderText="Name " />
                <asp:BoundField DataField="Country" HeaderText="Country" />
            </Columns>
        </asp:GridView>
        <asp:Button runat="server" Text="Count Checked Rows" OnClick="CountCheckedRows" />
        <br />
        <br />
        Click on Button to see count of checked CheckBox in GridView
        <asp:Label ID="lblCountedCheckBox" runat="server" />
    </div>
    </form>

C#:

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            DataTable dt = new DataTable();
            dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)),
                            new DataColumn("Name", typeof(string)),
                            new DataColumn("Country",typeof(string)) });
            dt.Rows.Add(1, "John Hammond", "United States");
            dt.Rows.Add(2, "Mudassar Khan", "India");
            dt.Rows.Add(3, "Suzanne Mathews", "France");
            dt.Rows.Add(4, "Robert Schidner", "Russia");
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }

    protected void CountCheckedRows(object sender, EventArgs e)
    {
        int count = 0;
        foreach (GridViewRow row in this.GridView1.Rows)
        {
            CheckBox chkId = (row.FindControl("chkId") as CheckBox);
            if (chkId.Checked)
            {
                count++;
            }
            this.lblCountedCheckBox.Text = count.ToString();
        }
    }

Thank You.