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

Ex Input:
Sentence: 'seagulls sit on the posts of a seaside balcony by a clock tower'. Find frequency of the letter 'g'

Ex Output:
1

Ex Input:
Sentence: 'two baseball players high five each other during a game'. Find frequency of the letter 'y'

Ex Output:
1

Ex Input:
Sentence: 'a cake in the shape of a toilet with andy 50 today written on it'. Find frequency of the letter 'h'

Ex Output:
3