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

Ex Input:
Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'town clocks affixed to a tall, brick building'. Find frequency of the letter 'r'

Ex Output:
1


Ex Input:
Sentence: 'a black and white cat standing over a water bowl'. Find frequency of the letter 's'

Ex Output:

1