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 riding on top of a wave on a surfboard'. How many words start with the letter 'o' in the sentence.
Example Output: 3

Example Input: Sentence: 'a group of boats floating in the ocean next to a dirty walkway'. How many words start with the letter 't' in the sentence.
Example Output: 2

Example Input: Sentence: 'close up from behind of a young giraffe standing with front legs splayed and head the ground by a fence outside'. How many words start with the letter 'f' in the sentence.
Example Output:
3