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

Input: Consider Input: Sentence: 'a woman cross country skiing in a competition'. Find frequency of the letter 's'

Output: 3

Input: Consider Input: Sentence: 'a table topped with a cupcake on a picture of a cupcake'. Find frequency of the letter 'o'

Output: 3

Input: Consider Input: Sentence: 'a man in a sweatshirt is taking his own picture'. Find frequency of the letter 'u'
Output: 1