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

Input: Consider Input: Sentence: 'a view from a bathroom shows an open door'. Find frequency of the letter 'o'

Output: 7

Input: Consider Input: Sentence: 'a green bus driving in a street filled with heavy traffic'. Find frequency of the letter 'v'

Output: 2

Input: Consider Input: Sentence: 'a person is performing a stunt on a snowboard'. Find frequency of the letter 'p'
Output: 2