[gmx-users] Newbie question

[Andres Rojas Guerrero]

Hi, I'm newbie in Gromacs and MD, I'm reading the Tsjerk excellent  
tutorial. In the part of Addition of Ions, Tsjerk said that we need to  
edit the topology file and the decrease the number of solvent molecules,  
and add a line specifying the number Na+ and Cl-. How can I do this?  Let  
me explain, in the topology file I have:

  [ molecules ]
10565 ; Compound        #mols
10566 Protein_A           1
10567 SOL               198
10568 SOL             10277

What number I need to change? and what it's the fomat to add the ions Na+  
and Cl- to topology file?

Thank you very much.

Andres.