Given a character array, s, representing a sentence, return a, the arithmetic mean of the number of letters per word in the given sentence. Round your answer to three decimal digits.

You may make the following assumptions:

1. All characters in the array are either letters or spaces.

2. There are no redundant spaces.

3. Except for spaces, there is no punctuation in the sentence.

4. There will always be at least two words in the sentence.

Example:

c = 'The quick brown fox jumps over the lazy dog';

a = 3.889;

Example:

c = 'Another one bites the dust';

a = 4.400;

The next problem in this series is Problem 44853.