I was wondering whast are URL parameters for DeepL automatic language detection?

For example, if I want to translate from English to Russian I can put this in the address bar:

https://www.deepl.com/en/translator#en/ru/Hello

But what is the source language is unknown? What should I pass in the URL for DeepL to detect the source language automatically? Something like

https://www.deepl.com/en/translator#auto/ru/Hello ??