Import data from excel to database

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.NET4

The below is my code to import data from excel to database.But when i enter new data in excel and uploading it to database all the data is again inserting into database.My requirement is only newly inserted file in excel should be upload to database

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using Microsoft.Office.Interop.Excel;
using System.Text;
using System.Reflection;
using System.Data.OleDb;
using System.Data;
using System.Data.SqlClient;
using System.Web.Security;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class apload : System.Web.UI.Page
{
    // int count = 0;
    string sName = "";
    DataSet ds = new DataSet();
    SqlDataAdapter adapter = new SqlDataAdapter();
    cnt1 cn = new cnt1();

    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnUpload_Click(object sender, EventArgs e)
    {
        int n = cn.upd();
        if (FileUpload1.HasFile)
        {
            sName = FileUpload1.FileName;
            Console.Write(sName);

            string ext = System.IO.Path.GetExtension(sName);

            if (ext == ".xls")
            {
                FileUpload1.SaveAs(Server.MapPath("../App_Data/" + "Books" + ext));

            }

        }
        sName = FileUpload1.FileName.ToString();
        OleDbConnection conn = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0; Data Source=D:\\" + sName + "; Extended Properties=\"Excel 8.0;HDR=YES\"");
        OleDbCommand cmd = new OleDbCommand("select * from [Sheet1$]", conn);
        //cmd.Connection = conn;
        //OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
        //DataSet ds = new DataSet();
        //adapter.Fill(ds, "ex");
        //count = ds.Tables["ex"].Rows.Count;
        //gdvEx.DataSource = ds;
        //gdvEx.DataBind();
        //int count = ds.Tables["ex"].Rows.Count;
        //for (int i = 0; i <= count; i++)
        //{


        //}
        try
        {
            //After connecting to the Excel sheet here we are selecting the data using select statement from the Excel sheet
            OleDbCommand ocmd = new OleDbCommand("select * from [Sheet1$]", conn);

            conn.Open();
            ocmd.Connection = conn;
            OleDbDataAdapter adapter = new OleDbDataAdapter(ocmd);
            DataSet ds = new DataSet();
            adapter.Fill(ds, "ex");
            int cnt = ds.Tables["ex"].Rows.Count;
            gdvEx.DataSource = ds;
            gdvEx.DataBind();
            //deletedatafromsql();
            //Here [Sheet1$] is the name of the sheet in the Excel file where the data is present
            OleDbDataReader odr = ocmd.ExecuteReader();
            string EmployeeID;
            string FirstName = "";
            string LastName = "";
            string Address = "";
            string Gender = "";

            while (odr.Read())
            {
                EmployeeID = valid(odr, 0);//Here we are calling the valid method
                FirstName = valid(odr, 1);
                LastName = valid(odr, 2);
                Address = valid(odr, 3);
                Gender = valid(odr, 4);

                //Here using this method we are inserting the data into the database
                if ((int)cnt != n)
                {
                    insertdataintosql(EmployeeID, FirstName, LastName, Address, Gender);
                }

           }
            conn.Close();
        }

        catch (DataException ee)
        {
            lblmsg.Text = ee.Message;
            lblmsg.ForeColor = System.Drawing.Color.Red;
        }
        finally
        {
            lblmsg.Text = "Data Inserted Sucessfully";
            lblmsg.ForeColor = System.Drawing.Color.Green;
        }
    }

    private string valid(OleDbDataReader myreader, int stval)//if any columns are 
    //found null then they are replaced by zero
    {
        object val = myreader[stval];
        if (val != DBNull.Value)
            return val.ToString();
        else
            return Convert.ToString(0);
    }

    public void insertdataintosql(string EmployeeID, string FirstName, string LastName, string Address, string Gender)
    {
        //inserting data into the Sql Server
        SqlConnection con = new SqlConnection("Server=SREEKANTH-MSFT\\SQLEXPRESS;Database=Example;Integrated Security=True");
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        // cmd.CommandText = "select * from Employee";

        cmd.CommandText = "insert into Employee(EmployeeID,FirstName,LastName,Address,Gender)values(@EmployeeID,@FirstName,@LastName,@Address,@Gender)";
        cmd.Parameters.Add("@EmployeeID", SqlDbType.NVarChar).Value = EmployeeID;
        cmd.Parameters.Add("@FirstName", SqlDbType.NVarChar).Value = FirstName;
        cmd.Parameters.Add("@LastName", SqlDbType.NVarChar).Value = LastName;
        cmd.Parameters.Add("@Address", SqlDbType.NVarChar).Value = Address;
        cmd.Parameters.Add("@Gender", SqlDbType.NVarChar).Value = Gender;
        cmd.CommandType = CommandType.Text;
        con.Open();
        cmd.ExecuteNonQuery();
        con.Close();
    }
    
}