Given three arrays of integers, return the sum of elements that are common in all three arrays.
For example: 
```
common([1,2,3],[5,3,2],[7,3,2]) = 5 because 2 & 3 are common in all 3 arrays
common([1,2,2,3],[5,3,2,2],[7,3,2,2]) = 7 because 2,2 & 3 are common in the 3 arrays
```
More examples in the test cases. 
Good luck!
def common(a,b,c):
    d = set(a)&set(b)&set(c)
    a = [i for i in a if i in d]
    b = [i for i in b if i in d]
    c = [i for i in c if i in d]
    return sum([i*min(a.count(i), b.count(i), c.count(i)) for i in d])
def common(a,b,c):
    d = set(a)&set(b)&set(c)
    a = [i for i in a if i in d]
    b = [i for i in b if i in d]
    c = [i for i in c if i in d]
    return sum([i*min(a.count(i), b.count(i), c.count(i)) for i in d])