i got lots of files like this:

```
./1/wwuhw.mp3
./2/nweiewe.mp3
./3/iwqjoiw.mp3
./4/ncionw.MP3
./5/joiwqfm.wmv
./6/jqoifiew.WMV

```

how can i rename them like this in Linux Bash:

```
./1/1.mp3
./2/2.mp3
./3/3.mp3
./4/4.MP3
./5/5.wmv
./6/6.WMV

```