explicit is better than implicit!  The only thing I'd suggest is figuring out how to combine your `if` conditionals when they're chained like this:

```
 if big>=max_big:
    if small >= (goal-(max_big*5)):
```

This could simplify to:

```
 if big >= max_big and small >= (goal-(max_big*5)):
```

Slightly less readable but better style to consolodate conditionals when that's reasonable.