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

Ex Input:
Sentence: 'the street sign is next to a curved road'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'a railroad train pulling up to the train platform'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'some zebras dirt green grass plants and bushes'. Find frequency of the letter 'b'

Ex Output:

2