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

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

Ex Output:
3


Ex Input:
Sentence: 'a baby calf has a tag on its right ear'. Find frequency of the letter 'n'

Ex Output:
1


Ex Input:
Sentence: 'man and woman touch hands going different directions on a surfboard'. Find frequency of the letter 'd'

Ex Output:

5