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

Ex Input:
Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'a man riding a white surfboard on a large wave'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'an ana air plane is parked at the port'. Find frequency of the letter 'a'

Ex Output:

7