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

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 men are in a kitchen cooking and cutting through a dish'. Find frequency of the letter 'a'

Ex Output:
4

Ex Input:
Sentence: 'group of elephants feeding in between a row of trees in the jungle'. Find frequency of the letter 'o'

Ex Output:
4