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

Ex Input:
Sentence: 'a bathroom that has it's lights turned on'. Find frequency of the letter 'h'

Ex Output:
4


Ex Input:
Sentence: 'an area that has surrounded by a metal fence'. Find frequency of the letter 'o'

Ex Output:
1


Ex Input:
Sentence: 'a boat with it's light on in the water on a cloudy day'. Find frequency of the letter 'r'

Ex Output:

1