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

Ex Input:
Sentence: 'a group of people seated in chairs together and facing the same direction, with one man holding a soccer ball in his hands'. Find frequency of the letter 'm'

Ex Output:
2

Ex Input:
Sentence: 'a woman is taking a sip of a drink from a glass'. Find frequency of the letter 'i'

Ex Output:
4

Ex Input:
Sentence: 'a couple of wooden benches next to a stone wall'. Find frequency of the letter 'c'

Ex Output:
2