def NOA_metric(bpmn_graph):
activities_counts = get_activities_counts(bpmn_graph)<EOL>return activities_counts["<STR_LIT>"] + activities_counts["<STR_LIT>"]<EOL>
Returns the value of the NOA metric (Number of Activities)
for the BPMNDiagramGraph instance.

:param bpmn_graph: an instance of BpmnDiagramGraph representing BPMN model.