Concatenating nested strings

Write a function nested_concat that concatenates the strings in an arbitrarily nested list. It should take a list or string as input, and return a string as output. Our tester will only give you appropriate inputs.

Examples

>>> nested_concat([])
''
>>> nested_concat(['hello', 'world'])
'helloworld'
>>> nested_concat([[[['help'],'i'],['am', 'stuck'],'in'],'a','list'])
'helpiamstuckinalist'