Troubles with the installation of R on Ubuntu 18.04

I have this version of Ubuntu

Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.3 LTS
Release:	18.04
Codename:	bionic

on my computer in a dual boot with Windows. I have tried to install R following this tutorial https://www.digitalocean.com/community/tutorials/how-to-install-r-on-ubuntu-18-04 and I got the following error:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 r-base : Depends: r-base-core (>= 3.6.2-1bionic) but it is not going to be installed
          Depends: r-recommended (= 3.6.2-1bionic) but it is not going to be installed
          Recommends: r-base-html but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

To fix the error I followed this answer https://askubuntu.com/questions/140246/how-do-i-resolve-unmet-dependencies-after-adding-a-ppa but none of the proposed solution works. In partcular, even if my

apt-get -f install

returns

upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

, if I try again

apt install r-base

it's still not working