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

Ex Input:
Sentence: 'a man standing in front of a statue near a metal pole'. Find frequency of the letter 'f'

Ex Output:
2

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

Ex Output:
5

Ex Input:
Sentence: 'batter taking a swing at ball during game'. Find frequency of the letter 'n'

Ex Output:
3