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

Input: Consider Input: Sentence: 'a group of men standing on the side of a boat'. Find frequency of the letter 'o'

Output: 5

Input: Consider Input: Sentence: 'an old glass vase containing flowers on a glass table'. Find frequency of the letter 'b'

Output: 1

Input: Consider Input: Sentence: 'herd of sheep wandering around rocky area in countryside'. Find frequency of the letter 'n'
Output: 5