15/15 Median.

it appeared 'Oops, try again. median([4, 5, 5, 4]) returned 4 instead of 4.5'

I've been stuck here for a long time, could please someone help me to check my code, thanks!

```
def median(numbers):
r = numbers
r.sort()
if len(r) % 2 == 0:
return (r[len(r) / 2 - 1] + r[len(r) / 2]) / 2
else :
return r[(len(r) - 1 ) / 2]
```