Calculate the frequency of letter ‘a’ in the following sentence
This is a sentence
In the given sentence, the letter 'a' appears 1 time.
Complete the following task based on the instruction and optional input provided.### Instruction:
Calculate the frequency of letter ‘a’ in the following sentence

### Input:
This is a sentence

### Output:
In the given sentence, the letter 'a' appears 1 time.