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

Ex Input:
Sentence: 'a plane with smoke coming from the tips of both wings'. Find frequency of the letter 'c'

Ex Output:
1

Ex Input:
Sentence: 'the skateboarder has on red and black sneakers and is riding a skateboard'. Find frequency of the letter 'g'

Ex Output:
1

Ex Input:
Sentence: 'a woman stands in front of an open laptop'. Find frequency of the letter 'p'

Ex Output:
3