nonil = (summa = a+b+c).nil? rescue true
unless nonil
summa
end
/export file=flash/resetBackup
/system script add name=reset-backup source={/system reset-configuration keep-users=yes no-defaults=yes run-after-reset=flash/resetBackup.rsc}
/system routerboard mode-button set on-event=reset-backup enabled=yes
/synchronize