Nested Dict Lookup

Given a nested dict and list of keys, traverse and return value. Example: {'a':{'b':1}}, ['a','b'] => 1. Return None if path invalid.

Your task

Implement this function:

def nested_lookup(d: dict, keys: list):

Write the function only — the arguments are read for you and the return value is printed automatically.

Arguments arrive as one Python literal per line, in this order: d, keys.

Example

Input

{'a': {'b': 1}}
['a', 'b']

Output

1