Design a calculator capable of performing four operations:
- Addition `+`.
- Subtraction `-`.
- Multiplication `*`.
- Division `/`.
with two real numbers $a, b$.
### Input
- One line containing a real number $a$, a character representing the operation, and finally another real number $b$.
### Output
- Print the result of the operation. Round the result to the third decimal place. If the calculation is invalid, print `ze`.
### Constraints
- $-1000 \le a, b \le 1000$.
### Sample
Input:
```
4 * 5
```
Output:
```
20.000
```
