Find the observed frequency of the letter "s" in the sentence

The cat ran up the stairs
The observed frequency of the letter "s" in the sentence "The cat ran up the stairs" is 2.
Complete the following task based on the instruction and optional input provided.### Instruction:
Find the observed frequency of the letter "s" in the sentence

The cat ran up the stairs

### Output:
The observed frequency of the letter "s" in the sentence "The cat ran up the stairs" is 2.