Display Yes No Confirmation Box based on ASP.Net DropDownList selected value in C#

Hi,

I am trying to use Yes No Confirmation Message Box if i would like to use is a DropDownList.

I need Yes No Confirmation Message Box in DropDownList only if the value selected is equal to 3.

How can i modify the code?

My complete code below

<asp:DropDownList ID="ddl" Width="300px" runat="server" onchange="Confirm()" AppendDataBoundItems="true"
        OnSelectedIndexChanged="ddl_SelectedIndexChanged" AutoPostBack="true">
    <asp:ListItem Text="test1" Value="test1"></asp:ListItem>
    <asp:ListItem Text="test2" Value="test2"></asp:ListItem>
    <asp:ListItem Text="test3" Value="test3"></asp:ListItem>
</asp:DropDownList>

<script type="text/javascript">
    function Confirm() {
        var confirm_value = document.createElement("INPUT");
        confirm_value.type = "hidden";
        confirm_value.name = "confirm_value";
        if (confirm("Do you want to save data?")) {
            confirm_value.value = "Yes";
        } else {
            confirm_value.value = "No";
        }
        document.forms[0].appendChild(confirm_value);
    }
</script>

public void ddl_SelectedIndexChanged(object sender, EventArgs e)
{
    string confirmValue = Request.Form["confirm_value"];
    if (confirmValue == "Yes")
    {
        this.Page.ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('You clicked YES!')", true);
    }
    else
    {
        this.Page.ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('You clicked NO!')", true);
    }
}