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

Ex Input:
Sentence: 'a herd of zebra standing on top  of a grass covered field'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'a notebook and pen are left on a park bench'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'a woman with a red shirt is blow drying her hair'. Find frequency of the letter 'd'

Ex Output:

2