Generate Sequence Number and save it to a file in Asp.net

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using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using System.IO;

namespace Generate_id

{

public partial class _Default : System.Web.UI.Page

{

protected void generateid_Click(object sender, EventArgs e)

{

TextBox1.Text = GenerateSequenceNumber().ToString();

}

private int GenerateSequenceNumber()

{

string s2 = (Server.MapPath("test.txt"));

FileInfo fiRead = new FileInfo(s2);

string input = string.Empty;

int n1 = 1;

if (fiRead.Exists)

{

input = File.ReadAllText(s2);

}

if (input != string.Empty)

{

n1 = Convert.ToInt32(input);

}

File.WriteAllText(s2, (n1 + 1).ToString());

return n1;

}

}

}

Thanks