Plone Set Up Error

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W: GPG error: http://mirror.cs50.net InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 13F06945906AE267
W: Size of file /var/lib/apt/lists/ppa.launchpad.net_git-core_ppa_ubuntu_dists_trusty_main_binary-amd64_Packages.gz is not what the server reported 3398 3401
W: Size of file /var/lib/apt/lists/ppa.launchpad.net_git-core_ppa_ubuntu_dists_trusty_main_binary-i386_Packages.gz is not what the server reported 3394 3399
"
This is what I got when running sudo apt-get update
I am running all this on ide.c9.i0 for fixing a couple of bugs in Plone for Google summer of code program. i am not really experienced in Plone.
What do I different..?