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

Ex Input:
Sentence: 'a woman cross country skiing in a competition'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'a man riding on the back of a white horse next to other horses'. Find frequency of the letter 'o'

Ex Output:
6


Ex Input:
Sentence: 'a giraffe and several zebra in tail brush'. Find frequency of the letter 'v'

Ex Output:

1