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

Ex Input:
Sentence: 'two laptop computers sitting on top of a white table'. Find frequency of the letter 'f'

Ex Output:
1


Ex Input:
Sentence: 'three woman are having a discussion in the kitchen'. Find frequency of the letter 'n'

Ex Output:
5


Ex Input:
Sentence: 'a train is being boarded by passengers by a platform'. Find frequency of the letter 'a'

Ex Output:

6