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 touching a bird on top of a cage'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a photograph of a vase through its glass showcase'. How many words start with the letter 'i' in the sentence.
Example Output: 1

Example Input: Sentence: 'a man with a backpack skiing down a snowy slope'. How many words start with the letter 'a' in the sentence.
Example Output:
3