You can simplify `foo = foo + ...` to just `foo += ...`.

For example you can simplify the following two lines:

> ```
> m = m + 1
> ```

```
m += 1
```

> ```
> total = total + tenttotal + ref[roman[m]] - negtotal
> ```

```
total += tenttotal + ref[roman[m]] - negtotal
```