Show post number instead of page number

Hello,
I’ll try to explain what I’d like to do with an example.

Currently the following text is displayed: “Page 2 of 3”.
So if I have 4 posts per page and a sum of 10 posts, I’d like to change it to “Posts 5-8 of 10”.

As far as I can understand, I can’t do it without code changes, since I only see CURRENT_PAGE & TOTAL_PAGES parameters. So, what should I change in code to make it work like this?

Thanx!!

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