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

Ex Input:
Sentence: 'two giraffes standing next to some trees'. Find frequency of the letter 'f'

Ex Output:
2

Ex Input:
Sentence: 'city two way street with cars lined up on both sides'. Find frequency of the letter 'h'

Ex Output:
2

Ex Input:
Sentence: 'a woman kneeling down next to a fire hydrant with cans of paint'. Find frequency of the letter 'o'

Ex Output:
4