I know this question has been asked lots of times, but I am not asking how to remove duplicate elements from a list only, I want to remove the duplicated element as well.

For example, if I have a list:

```
x = [1, 2, 5, 3, 4, 1, 5]

```

I want the list to be:

```
x = [2, 3, 4] # removed 1 and 5 since they were repeated

```

I can't use a `set`, since that will include `1` and `5`.

Should I use a `Counter`? Is there a better way?