def all_activities_count(bpmn_graph):
return sum([<EOL>count for name, count in get_activities_counts(bpmn_graph).items()<EOL>])<EOL>
Returns the total count of all activities in the BPMNDiagramGraph instance.

:param bpmn_graph: an instance of BpmnDiagramGraph representing BPMN model.
:return: total count of the activities in the BPMNDiagramGraph instance