>>> from collita import extra

---- inici
>>> lCamp1 = [ (340, 130), (210, 230), (190, 140), 'pedra', (120, 190), (130, 210) ]
>>> r = extra(lCamp1)
>>> r
(740, 3, 250, 2)
>>> lCamp2 = [ (340, 130), (210, 230), 'pedra', (100, 210), 'pedra', (50, 140) ]
>>> r = extra(lCamp2)
>>> r
(-1, -1, -1, -1)
>>> lCamp3 = [ (120, 190), (130, 210), 'pedra', (340, 130), (210, 230), (190, 140) ]
>>> r = extra(lCamp3)
>>> r
(250, 2, 740, 3)

---- fi

No hi ha collita després de la 'pedra':
---------------------------------------
>>> lCamp4 = [ (200, 500), (100, 600), (300, 300), 'pedra']
>>> r = extra(lCamp4)
>>> r
(600, 3, 0, 0)

Només una collita abans i després de la 'pedra':
------------------------------------------------
>>> lCamp5 = [ (210, 150), 'pedra', (110, 180) ]
>>> r = extra(lCamp5)
>>> r
(210, 1, 110, 1)