Show alert message when reached to last page in Paginated GridView in ASP.Net

I have a gridview and two buttons Save and Next. On Save Button Click I am able to save each row of GridView and on Next Button I am able to call GridView_PageIndexChanging method but the problem is as under:-

On last Page index reached I am not able to dispaly a message like "You have"

//Design of Gridview is

<asp:GridView ID="gvStudents" runat="server" AutoGenerateColumns="False" AllowPaging="True"
    OnPageIndexChanging="gvStudents_PageIndexChanging" OnPageIndexChanged="gvStudents_PageIndexChanged"
    OnRowDataBound="gvStudents_RowDataBound" DataKeyNames="staff_id" EnablePersistedSelection="True"
    EmptyDataText="<p>You Have no Data</p>">
    <Columns>
        <asp:TemplateField HeaderText="Staff_id">
            <ItemTemplate>
                <asp:Label ID="lblstaffid" runat="server" Text='<%#Eval("staff_id") %>'></asp:Label></ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Name">
            <ItemTemplate>
                <asp:Label ID="lblstaffname" runat="server" Text='<%#Eval("name") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Father's Name">
            <ItemTemplate>
                <asp:Label ID="lblfname" runat="server" Text='<%#Eval("fname") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="In Time (Optional)">
            <ItemTemplate>
                <asp:DropDownList ID="ddlInTime" runat="server" AutoPostBack="true">
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Out Time(Optional)">
            <ItemTemplate>
                <asp:DropDownList ID="ddlOutTime" runat="server">
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Attendence">
            <ItemTemplate>
                <asp:DropDownList ID="AttendanceOption" runat="server">
                    <asp:ListItem Selected="True" Text="Present"></asp:ListItem>
                    <asp:ListItem Text="Absent"></asp:ListItem>
                    <asp:ListItem Text="Half Day Present"></asp:ListItem>
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Remarks">
            <ItemTemplate>
                <asp:TextBox ID="txtremarks" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

//End of Design of Gridview

//Design for two buttons

<asp:UpdatePanel ID="PanelGridData" runat="server">
    <Triggers>
        <asp:PostBackTrigger ControlID="btnSave" />
        <asp:PostBackTrigger ControlID="btnNext" />
    </Triggers>
</asp:UpdatePanel>
<asp:Button ID="btnSave" runat="server" Text="Save" OnClick="SaveStudentAttendance"
    CausesValidation="False" />&nbsp;&nbsp;
<asp:Button ID="btnNext" runat="server" Text="Next" CausesValidation="False" OnClick="btnNext_Click"
    Width="66px" />

//End of Design for buttons

//Code to Save each row of Gridview

foreach (GridViewRow row in gvStudents.Rows)
{
    if (row.RowType == DataControlRowType.DataRow)
    {
        string Astatus = ((row.FindControl("AttendanceOption") as DropDownList).SelectedItem.ToString());
        float staffId = float.Parse((row.FindControl("lblstaffid") as Label).Text.Trim());
        string Name = ((row.FindControl("lblstaffname") as Label).Text.Trim());
        string FName = ((row.FindControl("lblfname") as Label).Text.Trim());
        string attendenceDate = (this.txtselectDate.Text.Trim());
        string Remarks = ((row.FindControl("txtremarks") as TextBox).Text.Trim());
        string InTime = ((row.FindControl("ddlInTime") as DropDownList).SelectedItem.ToString());
        string OutTime = ((row.FindControl("ddlOutTime") as DropDownList).SelectedItem.ToString());
        string constring = System.Configuration.ConfigurationManager.ConnectionStrings["AISConnectionString"].ConnectionString;
        using (SqlConnection con1 = new SqlConnection(constring))
        {
            string query = "INSERT INTO d_attendance(staff_id,name,fname,dept,c_date,inTime,outTime,status,remarks) VALUES('" + staffId + "','" + Name + "', '" + FName + "', '" + lblsession.Text + "','" + attendenceDate + "','" + InTime + "','" + OutTime + "','" + Astatus + "','" + Remarks + "')";
            using (SqlCommand cmd = new SqlCommand(query, con1))
            {
                con1.Open();
                cmd.ExecuteNonQuery();
                //Response.Write("<script>alert('Attendance Data Saved for First Page Index. Proceed to next Page Index ')</script>");
                lblnotify.Text = "Attendance Data Saved. Please Click Next";
                con1.Close();
                btnSave.Enabled = false;
                btnNext.Enabled = true;
                txtselectDate.Enabled = true;
            }
        }
    }
}

//End of Code to save each row of grid

//Code behind Next Button

protected void btnNext_Click(object sender, EventArgs e)
{
    int a = gvStudents.PageCount;
    try
    {
        if (gvStudents.PageIndex < a)
        {
            gvStudents.PageIndex = gvStudents.PageIndex + 1;
            lblnotify.Text = "";
            PopulateStudentDetails();
            btnSave.Enabled = true;
            btnNext.Enabled = false;
        }
    }
    catch (Exception ex)
    {
        if (gvStudents.PageIndex >= a)
        {
            lblnotify.Text = "You have reached end of grid";
            btnNext.Enabled = false;
            btnSave.Enabled = false;
        }
    }
}

Please help me I am not able to display message on last page of gridview.