Get count of selected items in ASP.Net ListBox using C#

Refer this

HTML

<div>
    <asp:ListBox ID="lbFruits" runat="server" SelectionMode="Multiple" Width="200" Height="150">
        <asp:ListItem Text="Mango" Value="Mango" />
        <asp:ListItem Text="Banana" Value="Banana" />
        <asp:ListItem Text="Apple" Value="Apple" />
        <asp:ListItem Text="Orange" Value="Orange" />
        <asp:ListItem Text="Guava" Value="Guava" />
        <asp:ListItem Text="Strawberry" Value="Strawberry" />
        <asp:ListItem Text="Pineapple" Value="Pineapple" />
        <asp:ListItem Text="Jackfruit" Value="Jackfruit" />
    </asp:ListBox>
    <hr />
    <asp:Button Text="Count Selected option" OnClick="CountSelectedOption" runat="server" />
</div>

C#

protected void CountSelectedOption(object sender, EventArgs e)
{
    int count = 0;
    foreach (ListItem  item in this.lbFruits.Items)
    {
        if (item.Selected)
        {
            count++;
        }
    }
    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Selected option count = " + count + "')", true);
}

Screenshot