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

Input: Consider Input: Sentence: 'this is a sign in front of a large cathedral'. Find frequency of the letter 'a'

Output: 5

Input: Consider Input: Sentence: 'a group of people having dinner and drinking wine'. Find frequency of the letter 'r'

Output: 3

Input: Consider Input: Sentence: 'an area that has surrounded by a metal fence'. Find frequency of the letter 'o'
Output: 1