>>> from primvols import primer_vol

---- inici

>>> lv = ['BCN',8,9,12,14,15,18,20,21]
>>> primer_vol(lv,'BCN',16)
18
>>> primer_vol(lv,'BCN',14)
14
>>> primer_vol(lv,'BCN',22)
-1
>>> primer_vol(lv,'SEV',14)
-1

---- fi

>>> primer_vol(lv,'BCN',10)
12
>>> primer_vol(lv,'BCN',19)
20
>>> primer_vol(lv,'BCN',7)
8