Your company has an on-premises network and three Azure subscriptions named Subscription1, Subscription2, and Subscription3.
The departments at the company use the Azure subscriptions as shown in the following table.

All the resources in the subscriptions are in either the West US Azure region or the West US 2 Azure region.
You plan to connect all the subscriptions to the on-premises network by using ExpressRoute.
What is the minimum number of ExpressRoute circuits required?