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

Ex Input:
Sentence: 'a couple of boys in a field playing baseball'. Find frequency of the letter 'i'

Ex Output:
3


Ex Input:
Sentence: 'a white police vehicle parked on a paved street'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a grey and white cat is looking up'. Find frequency of the letter 'e'

Ex Output:

2