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.

Example Input: Sentence: 'a group of people standing around an airplane on top of a field'. How many words start with the letter 'a' in the sentence.
Example Output: 5

Example Input: Sentence: 'a little white airplane that is parked on some concrete'. How many words start with the letter 'p' in the sentence.
Example Output: 1

Example Input: Sentence: 'a person on a snowboard on a snowy day'. How many words start with the letter 'a' in the sentence.
Example Output:
3