Solve the programming task below in a Python markdown code block.
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
```
Also feel free to reuse/extend the following starter code:
```python
def repeat_sum(l):
```