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

Ex Input:
Sentence: 'pedestrians pass by a stop sign, some holding surfboards'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a close up of a plate with a whole carrot'. Find frequency of the letter 'w'

Ex Output:
2


Ex Input:
Sentence: 'a truck parked on the dock as a boat approaches'. Find frequency of the letter 's'

Ex Output:

2