Custom Calendar

This way:

<form id="form1" runat="server">
    <div>
        Start Date
        <asp:TextBox ID="txtStartDate" runat="server" />
        <br />
        End Date
        <asp:TextBox ID="txtEndDate" runat="server" />
        <asp:Calendar ID="cldHolidays" runat="server" OnPreRender="cldHolidays_OnPreRender">
        </asp:Calendar>
        <br />
        <asp:Label ID="lblTotaolLeavs" runat="server" />
        <br />
        <asp:Button runat="server" OnClick="CalculateLeavesexcludingHolidays" Text="Calculate Leaves excluding Holidays" />
    </div>
    </form>

C#:

protected void cldHolidays_OnPreRender(object sender, EventArgs e)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3]{new DataColumn("Festival_Id",typeof(int)),
                                new DataColumn("Festival_Name",typeof(string)),
                                new DataColumn("Festival_Date",typeof(DateTime))});
        dt.Rows.Add(1, "Eid_ul_Fitr", "2014-07-28 00:00:00.000");
        dt.Rows.Add(1, "Eid_ul_Fitr", "2014-07-29 00:00:00.000");
        dt.Rows.Add(1, "Eid_ul_Fitr", "2014-07-30 00:00:00.000");
        dt.Rows.Add(1, "Eid_ul_Fitr", "2014-07-31 00:00:00.000");
        dt.Rows.Add(1, "Eid_ul_Fitr", "2014-08-01 00:00:00.000");
        dt.Rows.Add(1, "Eid_ul_Fitr", "2014-08-03 00:00:00.000");
        int maxRow = dt.Rows.Count - 1;
        DateTime startDate = Convert.ToDateTime(dt.Rows[0]["Festival_Date"]);
        DateTime endDate = Convert.ToDateTime(dt.Rows[maxRow]["Festival_Date"]);
        TimeSpan difference = endDate.Date - startDate.Date;

        cldHolidays.SelectedDates.Clear(); //Clear previously selected dates, if any
        for (int i = 0; i <= difference.Days; i++)
            cldHolidays.SelectedDates.Add(startDate.AddDays(i)); //Highlight the dates 
    }

    protected void CalculateLeavesexcludingHolidays(object sender, EventArgs e)
    {
        int count = 0;
        DateTime startDate = Convert.ToDateTime(this.txtStartDate.Text.Trim());
        DateTime endDate = Convert.ToDateTime(this.txtEndDate.Text.Trim());
        SelectedDatesCollection dates = cldHolidays.SelectedDates;
        DateTime i = startDate;
        for (i = startDate; i < endDate; i = i.AddDays(1))
        {
            if (dates.Contains(i))
            {
                count++;
            }
        }

        int leavs = Convert.ToInt32((endDate - startDate).ToString("dd")) - count;
        this.lblTotaolLeavs.Text = string.Format("Total Leaves excluding Holidays {0}", leavs.ToString());
    }

Thank You.