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

Ex Input:
Sentence: 'the sun goes down over a bike tied to a bench at the beach'. Find frequency of the letter 't'

Ex Output:
5


Ex Input:
Sentence: 'a red fire hydrant opened and spilling water'. Find frequency of the letter 'd'

Ex Output:
4


Ex Input:
Sentence: 'the surfer is riding a wave on his board'. Find frequency of the letter 'i'

Ex Output:

4