def TNE_metric(bpmn_graph):
events_counts = get_events_counts(bpmn_graph)<EOL>return sum(<EOL>[count for _, count in events_counts.items()]<EOL>)<EOL>
Returns the value of the TNE metric (Total Number of Events of the Model)
for the BPMNDiagramGraph instance.

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