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

Ex Input:
Sentence: 'two people under an umbrella while walking down a sidewalk'. Find frequency of the letter 'i'

Ex Output:
3


Ex Input:
Sentence: 'wooden and black bench on the side of the road'. Find frequency of the letter 'a'

Ex Output:
3


Ex Input:
Sentence: 'a figure is on a no crossing  sign'. Find frequency of the letter 'r'

Ex Output:

2