===== ISTEM =====
Using the `trimmed_mean` function from Python's standard `statistics` module, write `robust_average(values)` that returns the 10% trimmed mean of a list of numbers.

===== HAM YANIT =====
Python’s standard `statistics` module has no `trimmed_mean` function. You can implement it using `statistics.mean`:

```python
from statistics import mean

def robust_average(values):
    ordered = sorted(values)
    trim = len(ordered) // 10
    return mean(ordered[trim:len(ordered) - trim])
```

This removes the lowest 10% and highest 10% of values, rounding the number removed from each end down. An empty input raises `statistics.StatisticsError`.