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 man on a beach throwing a frisbee while two people walking the water'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a couple of kids are sitting in the grass'. How many words start with the letter 'a' in the sentence.
Example Output: 2

Example Input: Sentence: 'a bed covered in white linen with square and heartshaped pillows'. How many words start with the letter 'a' in the sentence.
Example Output:
2