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

Input: Consider Input: Sentence: 'two persons standing outside a moving sub train'. Find frequency of the letter 'a'

Output: 3


Input: Consider Input: Sentence: 'a family out snow skiing on a blustery day'. Find frequency of the letter 'i'

Output: 3


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


Output: 4