>>> from nomines import sou

>>> sou(1000,12,500)
905.0
>>> sou(1000,12,0)
880.0
>>> sou(1000,11.4,1350)
951.0
>>> sou(1000,11.4,1301)
951.0
>>> sou(1352,11.4,579)
1222.872
>>> sou(1352,11.4,499)
1217.872