Navigating to the page given shows a calculator, as described.

We tried a few things at first, like causing an error:

Or entering in a calculation that results in 0:

But after doing more research into the `eval()` function in Python - which was most likely doing this calculation work, we realised that it could probably be used to run some shellcode (ish). So we decided to use the `subprocess` module, which allows you to run shell code in Python.

```
__import__('subprocess').getoutput('ls')
```

gaves us this:

```
__pycache__ main.py prestart.sh templates test.txt
```

Printing out `main.py` via
```
__import__('subprocess').getoutput('ls')
```
Printed out the entire `main.py` script that powers the site. A notable variable is `maybe_this_maybe_not`, whose value is the flag.

**Flag**: `DUCTF{3v4L_1s_D4ng3r0u5}`
**Further reading**: [Dangerous Python functions, like `eval()` and the `subprocess` module](https://www.kevinlondon.com/2015/07/26/dangerous-python-functions.html)