In this task, you need to count the number of words in a sentence that start with the given letter. Answer with numbers and not words.

Let me give you an example: Sentence: 'a hot dog in a bun with ketchup on a plate with french fries'. How many words start with the letter 'a' in the sentence.
The answer to this example can be: 3
Here is why: The word 'a' is the only word that starts with 'a'. This sentence has 3 occurrences of the word 'a'. So, the answer is 3.

OK. solve this:
Sentence: 'a row of skis sitting up against a fence'. How many words start with the letter 'a' in the sentence.
Answer:
3