tldr:

- Understand the fortran code in `MAIN__()` which offsets the input bytes
- Note that arrays start from 1

```
bcactf{f0rtr4N_i5_c0oO0l}
```

[Python Script](flag_checker_decode.py)

Python script in writeup link

Original writeup (https://github.com/IRS-Cybersec/ctfdump/tree/master/BCACTF%202021/RE/Wait%2C%20this%20isn't%20C).