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

Ex Input:
Sentence: 'a person is performing a stunt on a snowboard'. Find frequency of the letter 'p'

Ex Output:
2

Ex Input:
Sentence: 'hotel towels with sunglasses perched and hotel business cards and catalog'. Find frequency of the letter 'o'

Ex Output:
4

Ex Input:
Sentence: 'a picture of a very nice that in a room'. Find frequency of the letter 'r'

Ex Output:
3