This is a basic linux question I think, but I really want to know.

For example, currently I am in `/usr/bin`:

```
[x@localhost bin]$ pwd
/usr/bin
[x@localhost bin]$ cd /
[x@localhost /]$

```

Now I want to go back to previous path `/usr/bin`, how to do that quickly? I don't want to type `cd /usr/bin` again.