# coding=utf-8
"""
We want make a package of goal kilos of chocolate. We have small bars (1 kilo each)
and big bars (5 kilos each). Return the number of small bars to use, assuming we always
use big bars before small bars. Return -1 if it can't be done.

make_chocolate(4, 1, 9) → 4
make_chocolate(4, 1, 10) → -1
make_chocolate(4, 1, 7) → 2
"""

def make_chocolate(small, big, goal):
  if goal>(big*5)+small:
    return -1
  elif goal==big*5:
    return 0
  elif goal<big*5:
    if goal-((goal//5)*5)>small:
      return -1
    else:
      return goal-((goal//5)*5)
  elif goal==(big*5)+small:
    return small
  elif goal>big*5:
    return goal-big*5
  else:
      pass

print(make_chocolate(4,1,9))
print(make_chocolate(4,1,10))
print(make_chocolate(4,1,7))
print(make_chocolate(6, 2, 7))