How can I make a sum of column showed by DBGrid???

I put in my aplication a DBGrid linked to a Query to find in a
database, Bills to pay between two dates, this SQL command:
Select * from Dados.Contas where Vencimento between  DataIni  and
DataFi order by Vencimento
This command return to DBGrid what I was looking for, but I need make a

sum from column Valor and I don=B4t know how do it....:^(((
The columns are:
Name ----------- string
Date ------------ date
vencimento--- date
valor ------------ currency

Can anyone help me??=20


    Luiz Claudio ( from Brazil )