Construct a GPT model capable of completing the addition and subtraction of two numbers.
Example: 8 - 4
The result of 8 - 4 is 4.
Complete the following task based on the instruction and optional input provided.### Instruction:
Construct a GPT model capable of completing the addition and subtraction of two numbers.

### Input:
Example: 8 - 4

### Output:
The result of 8 - 4 is 4.