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 bus is parked on the side of a road in front of a building'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a group gathering in which several people are holding frisbees'. How many words start with the letter 'g' in the sentence.
Example Output: 2

Example Input: Sentence: 'a close up of a pizza with cheese and mushrooms'. How many words start with the letter 'a' in the sentence.
Example Output:
3