Portfolio Wgts Optimization

Greeting,
     Apologies for the blank email...I am quite new to optim function
in R. I am trying to do the following:

     I am trying to optimize Portfolio wgts subjected to certain
constraints. The constraints are that individual weights can be either
0 or maximum 40% and that the sum of the weights should be 1.

      While I know that I can use L-BFGS-B method and specify the
lower & upper bound, How can I specify the constraint that the sum of
the weights should add up to 1?

     Thanks in advance for your help.

Cheers

Manoj