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

Ex Input:
Sentence: 'a man that is on his cell phone'. Find frequency of the letter 's'

Ex Output:
2


Ex Input:
Sentence: 'a man sitting on a motorcycle near two other men'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'three boats are moving swiftly down the river'. Find frequency of the letter 't'

Ex Output:

4