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

Ex Input:
Sentence: 'a woman is taking a sip of a drink from a glass'. Find frequency of the letter 'i'

Ex Output:
4


Ex Input:
Sentence: 'a yellow and green train on a train track in a wooded area'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'a boy sitting at a table with a doughnut and a bottle of water'. Find frequency of the letter 'w'

Ex Output:

2