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 group of young people riding snow boards down a snow covered hillside'. How many words start with the letter 'a' in the sentence.
Example Output: 2

Example Input: Sentence: 'a man on a surfboard in the midst of an ocean wave'. How many words start with the letter 'o' in the sentence.
Example Output: 3

Example Input: Sentence: 'a person mixing something in  a blender'. How many words start with the letter 'a' in the sentence.
Example Output:
2