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

Ex Input:
Sentence: 'two pepperoni pizzas and a cup on a counter'. Find frequency of the letter 'u'

Ex Output:
2


Ex Input:
Sentence: 'some sheep are standing in a grassy field'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'batter taking a swing at ball during game'. Find frequency of the letter 'n'

Ex Output:

3