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

Ex Input:
Sentence: 'the little girl is flying her kite in the field'. Find frequency of the letter 'i'

Ex Output:
7


Ex Input:
Sentence: 'three people are gathered around sitting on a park bench'. Find frequency of the letter 'g'

Ex Output:
2


Ex Input:
Sentence: 'a bear sits on the rocks by a pool of water in a wildlife exhibit'. Find frequency of the letter 'r'

Ex Output:

3