In this task, you need to count the number of times the given letter appears in the given sentence.

Input: Consider Input: Sentence: 'a baseball player dropping his bat and starting to run'. Find frequency of the letter 'o'

Output: 2

Input: Consider Input: Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'

Output: 3

Input: Consider Input: Sentence: 'some people are walking down a road holding kites'. Find frequency of the letter 'r'
Output: 2