>>> from flatrate import first_big_consump

>>> lclients= [['444B', 300, 70, 220, 120], ['333A', 40, 35, 50], 
... ['555C', 100, 30, 23, 130, 60]]
>>> first_big_consump(lclients)
'333A'
>>> lclients= [['444B', 300, 70, 220, 120], ['333A', 100, 35, 50], 
... ['555C', 200, 30, 23, 130, 60]]
>>> first_big_consump(lclients)
''