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

Input: Consider Input: Sentence: 'an image of a street sign with a corner restaurant'. Find frequency of the letter 'u'

Output: 1

Input: Consider Input: Sentence: 'a double-decker bus covered in children's illustrations driving next to a van'. Find frequency of the letter 'a'

Output: 4

Input: Consider Input: Sentence: 'a dog laying under a blanket in a bed'. Find frequency of the letter 'n'
Output: 4