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 without a shirt riding a skateboard'. How many words start with the letter 'r' in the sentence.
Example Output: 1

Example Input: Sentence: 'a zebra is running toward a shady area under the trees'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a man riding skis across snow covered ground'. How many words start with the letter 'a' in the sentence.
Example Output:
2