I will be staying in Noisy-Champs for 5 days in a mid of July. I will be arriving with an airplane on a Charles De Gaulle Airport. I saw that mostly I will use RER A and RER B (just from the airport twice, while coming and going back home) and also that this places lays under up to 5th zone for RER B, and 4th to 5th zone to RER A. Can someone confirm to me what is the best option for buying a ticket in this period?