Sum of Elements

Write a function that returns the sum of all the elements included in the root list.

Examples

func([ [], [] ,[] ]) ➞ 3
# 1 + 1 + 1 = 3
# The three empty lists inside the root list.

func([ [3], [2] ,[1,2] ]) ➞ 7
# 1 + 1 + 1 = 3
# The three lists inside the root list.
# 1 + 1 + 2 = 4
# The elements inside the previous lists.
# 4 + 3 = 7

func([]) ➞ 0
# The root list is empty thus there are no elements.

func([[[]]]) ➞ 2
# 1
# The only list in the root list.
# 1
# The empty list in the previous list.
# 1 + 1 = 2

Notes

If a list is empty return/add 0.