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

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 dog laying on the back of a boat in the water'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'a person stands in a group of sheep while a sheep herding dog crouches nearby'. Find frequency of the letter 'o'

Ex Output:

5