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

Ex Input:
Sentence: 'a picture of two men on a motorcycle in front of a railroad track'. Find frequency of the letter 'n'

Ex Output:
4


Ex Input:
Sentence: 'two giraffes standing next to some trees'. Find frequency of the letter 'f'

Ex Output:
2


Ex Input:
Sentence: 'people are walking on a street with shops and a clock'. Find frequency of the letter 'p'

Ex Output:

3