The given sentence contains a typo which could be one of the following four types: (1) swapped letters of a word e.g. 'niec' is a typo of the word 'nice'. (2) missing letter in a word e.g. 'nic' is a typo of the word 'nice'. (3) extra letter in a word e.g. 'nicce' is a typo of the word 'nice'. (4) replaced letter in a word e.g 'nicr' is a typo of the word 'nice'. You need to identify the typo in the given sentence. To do this, answer with the word containing the typo.

Example Input: A re-crested wood-pecker on a lichen covered tree.
Example Output: re-crested

Example Input: three fishing boats in the water docked in the harbor
Example Output: None

Example Input: A mab in a multi-colored beanie pedals a passenger bike.
Example Output:
mab