C sharp - crear folio

public string creafolio()

{

    int i;

    string sql="select  max(id_cliente)  from tbl_ejemplo";

    i = int.Parse(sql);

    if (i >= 1)

    {

        i++;

        return i.ToString();

    }

    else

    {

        return i.ToString();

    }

}

USE [BASE DE DATOS]

GO

/****** Object:  StoredProcedure [dbo].[Proc_Agrega_Insumo]    Script Date: 16/10/2018 18:46:15 ******/

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

-- =============================================

-- Author:		<Marco A. Granados B.>

-- Create date: <21/05/2017>

-- Description:	<Generación de un nuevo número de Insumo>

-- =============================================

 PROCEDURE [dbo].[Proc_Agrega_Insumo]

-- Parámetros

    @InsumoDescripción nvarchar(50),

    @InsumoUDM nvarchar(5),

    @InsumoCosto money,

    @InsumoFecha nvarchar(20),

    @InsumoEstatus bit,

    @InsumoNotas nvarchar(Max)

AS

BEGIN

	DECLARE @InsumoId AS nvarchar(6), @Max_Número AS int

	SELECT @Max_Número = ISNULL(MAX(CAST(RIGHT([Insumos].[InsumoId],4) AS nvarchar)),0) + 1 FROM [dbo].[Insumos]

	SET @InsumoId = (SELECT 'IN' + REPLICATE('0',4-LEN(@Max_Número))+CAST(@Max_Número AS nvarchar(6)))

	INSERT INTO [dbo].[Insumos]

	VALUES (@InsumoId, @InsumoDescripción, @InsumoUDM, @InsumoCosto,@InsumoFecha, @InsumoEstatus,@InsumoNotas,'')

END

public string creafolio()

{

    cn.Open();

    int valorMax;

    string sql = "select  max(idCliente)  from tblClientes";

    comando = new SqlCommand(sql, cn);

    SqlDataReader folio = comando.ExecuteReader();

    folio.Read();

    if (folio.GetValue(0).ToString() == string.Empty)

    {

        cn.Close();

        valorMax = 1;

        return valorMax.ToString();

    }

    else

    {

        valorMax = int.Parse(folio.GetValue(0).ToString());

        cn.Close();

        valorMax++;

        return valorMax.ToString();

    }

}