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

Ex Input:
Sentence: 'a picture of a toilet and toilet paper in a bathroom'. Find frequency of the letter 'o'

Ex Output:
5


Ex Input:
Sentence: 'a stop sign near a rail road crossing sign'. Find frequency of the letter 'g'

Ex Output:
3


Ex Input:
Sentence: 'a person wearing blue catching a ball and a person with a red helmet on the ground'. Find frequency of the letter 'd'

Ex Output:

3