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

Ex Input:
Sentence: 'young boy flying kite in large field at outdoor event'. Find frequency of the letter 'y'

Ex Output:
3


Ex Input:
Sentence: 'two men with colorful ties are posing for a picture'. Find frequency of the letter 'r'

Ex Output:
4


Ex Input:
Sentence: 'here's a cute souvenir from the urban experience'. Find frequency of the letter 'e'

Ex Output:

9