Listbox - Number of selected items C# ASP.NET

While using listbox in c#, how can learn the count of selecteditems?

Listbox items: Denver, Chicago, Baltimora. For example, I select Chicago and Denver.

I want to make a loop in order to assign selecteditems.

How can I achieve it? How can I learn the number of selected item? I have tried using the code below. But when  I select Chicago and Denver the count value is 0...

Thank you

        string city = string.Empty;
        int count = 0;
        foreach (ListItem item in myddl.Items)
        {
            if (item.Selected)
            {
                count++;

                if(count == 1)
                {
                    city = item.Value.ToString() + ";";
                }
                else
                {
                    city += item.Value.ToString() + "; ";
                }
            }
        }

The listbox

                            <asp:ListBox ID="myddl" runat="server" SelectionMode="Multiple">
                                <asp:ListItem Text="[ ===  Select your City === ]" Value=""></asp:ListItem>
                                <asp:ListItem Text="Denver" Value="Denver"></asp:ListItem>
                                <asp:ListItem Text="Chicago" Value="Chicago"></asp:ListItem>
                                <asp:ListItem Text="Baltimora" Value="Baltimora"></asp:ListItem>
                            </asp:ListBox>