Write a function that takes a list comprised of other lists of integers and returns the sum of all numbers that appear in two or more lists in the input list.  Now that might have sounded confusing, it isn't:
```python
repeat_sum([[1, 2, 3],[2, 8, 9],[7, 123, 8]])
>>> sum of [2, 8]
return 10
repeat_sum([[1], [2], [3, 4, 4, 4], [123456789]])
>>> sum of []
return 0
repeat_sum([[1, 8, 8], [8, 8, 8], [8, 8, 8, 1]])
sum of [1,8]
return 9
```
from collections import Counter
from itertools import chain

def repeat_sum(l):
    return sum(key for key, value in Counter(chain.from_iterable(set(x) for x in l)).items() if value > 1)
from collections import Counter
from itertools import chain

def repeat_sum(l):
    return sum(key for key, value in Counter(chain.from_iterable(set(x) for x in l)).items() if value > 1)