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

Ex Input:
Sentence: 'cars parked outside if a retail store'. Find frequency of the letter 'd'

Ex Output:
2


Ex Input:
Sentence: 'silhouette of person playing frisbee with moutain and sunset'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'a man waling through a train rail yard with trains passing on either side of him'. Find frequency of the letter 'r'

Ex Output:

6