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 clock tower atop a tall building with a lighting rod'. How many words start with the letter 'a' in the sentence.
Example Output: 4

Example Input: Sentence: 'this grizzly bear is standing in some shallow water'. How many words start with the letter 'g' in the sentence.
Example Output: 1

Example Input: Sentence: 'three sheep standing together in a grassy field'. How many words start with the letter 's' in the sentence.
Example Output:
2