Public Key Is Not Avaiable

When you getting this problems usually when you update:

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 54422A4B98AB5139

The solution is simple.Take the first key you have problem with, for example E635A714505A2DD1, take the last 8 symbols (in this case - 505A2DD1) and run the following in the terminal:

gpg --keyserver keyserver.ubuntu.com --recv 505A2DD1

gpg --export --armor 505A2DD1 | sudo apt-key add -

Then repeat this step with every problematic key.