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

Ex Input:
Sentence: 'two bears swim in a blue pool of water'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'a person is holding a chocolate doughnut with rainbow sprinkles'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'the young woman is kicking a soccer ball into the air'. Find frequency of the letter 'a'

Ex Output:

4