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

Ex Input:
Sentence: 'a giraffe sticking it's tongue out near a window'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a woman swinging a tennis racquet towards a tennis ball'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'an airplane in mid-flight in a cloudless sky'. Find frequency of the letter 'i'

Ex Output:

5