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

Ex Input:
Sentence: 'a green bus driving in a street filled with heavy traffic'. Find frequency of the letter 'v'

Ex Output:
2


Ex Input:
Sentence: 'two women standing next to each other holding tennis rackets'. Find frequency of the letter 't'

Ex Output:
7


Ex Input:
Sentence: 'people gather at the beach with black umbrellas'. Find frequency of the letter 'l'

Ex Output:

4