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

Ex Input:
Sentence: 'a railroad train pulling up to the train platform'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'a birthday cake with a number one and three candle'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'these horses are pulling a cart with two men on it'. Find frequency of the letter 'o'

Ex Output:

3