Sorry to bylo špatně
Přidávání zdrojůedit:postup vytvoření klíče → What you need to do, is the following:
Open gnome-terminal and enter the following:
gpg --keyserver subkeys.pgp.net --recv C71839136CF5CE97
(replace "C71839136CF5CE97" by the code in your error message)
Then enter the following:
gpg --export --armor C71839136CF5CE97 | sudo apt-key add -
(here again, replace "C71839136CF5CE97" by the code in your error message)
Then, to finish off, enter the following:
sudo apt-get update