failed to convert parameter value from a string to a int32

protected void btnsubmit_Click(object sender, EventArgs e)
    {
        try
        {
            SqlConnection vcon = new SqlConnection(ConfigurationManager.ConnectionStrings["surendra"].ToString());

            vcon.Open();
            SqlCommand vcmd = new SqlCommand();
            vcmd.Connection = vcon;
            vcmd.CommandType = CommandType.StoredProcedure;
            vcmd.CommandText = "register_sp ";
            SqlParameter sp1 = new SqlParameter("@emailid", SqlDbType.VarChar, 100);
            sp1.Direction = ParameterDirection.Input;
            sp1.Value = Txteid.Text;
            vcmd.Parameters.Add(sp1);
            SqlParameter sp2 = new SqlParameter("@password", SqlDbType.Int);
            sp2.Direction = ParameterDirection.InputOutput;
            sp2.Value = Txtpwd.Text;
            vcmd.Parameters.Add(sp2);
            SqlParameter sp3 = new SqlParameter("@firstname", SqlDbType.VarChar, 100);
            sp3.Direction = ParameterDirection.Input;
            sp3.Value = txtfname.Text;
            vcmd.Parameters.Add(sp3);
            SqlParameter sp4 = new SqlParameter("@lastname", SqlDbType.VarChar, 100);
            sp4.Direction = ParameterDirection.Input;
            sp4.Value = Txtlname.Text;
            vcmd.Parameters.Add(sp4);
            vcmd.ExecuteNonQuery();
            Response.Write("http://www.facebook.com");
            vcon.Close();
        }
       catch(Exception ex)
        {

            Response.Write(ex.Message);
       }

ALTER procedure [dbo].[register_sp]
@emailid varchar(100),@password int,@firstname varchar(100),@lastname varchar(100)
as
insert into  Users(emailid,Password,firstname,lastname) values (@emailid,@password,@firstname,@lastname)
select * from users