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 time laps photo of a city street'. How many words start with the letter 'o' in the sentence.
Example Output: 1

Example Input: Sentence: 'people walking down the street while some people ride their bicycles'. How many words start with the letter 'w' in the sentence.
Example Output: 2

Example Input: Sentence: 'three people in a boat traveling down the river'. How many words start with the letter 'a' in the sentence.
Example Output:
1