Definition: In this task, you need to reverse all words of a given length in the sentence. The number of letters in a word determine its length. For example, the length of the word "apple" is 5.
Input: Sentence: 'small groups of people wander the beach watching the kites fly'. Reverse all words of length '8' in the given sentence.

small groups of people wander the beach gnihctaw the kites fly