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 brown and white cat laying on blanket on door of open oven'. How many words start with the letter 'o' in the sentence.
Example Output: 5

Example Input: Sentence: 'a train passes over a quiet city park on a bridge'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a guitar is leaning against a chair with a christmas tree visible in the side of the picture and toys on the ground in the front'. How many words start with the letter 's' in the sentence.
Example Output:
1