update eror

W: GPG error: http://packages.linuxmint.com isadora Release: The following
signatures couldn't be verified because the public key is not available:
NO_PUBKEY 3EE67F3D0FF405B2
W: GPG error: http://packages.medibuntu.org lucid Release: The following
signatures couldn't be verified because the public key is not available:
NO_PUBKEY 2EBC26B60C5A2783


$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0FF405B2

$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0C5A2783

$ sudo apt-get update