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

Input: Consider Input: Sentence: 'some sheep are standing in a grassy field'. Find frequency of the letter 'n'

Output: 3

Input: Consider Input: Sentence: 'a piece of film shows two street signs crossing each other'. Find frequency of the letter 'f'

Output: 2

Input: Consider Input: Sentence: 'an old truck is at the bottom of a small hill'. Find frequency of the letter 'm'
Output: 2