Installing a program from a mirror

[gemm]

Hi,

I am trying to install a program (R for statistical computing). I have added this line:

deb http://cran.at.r-project.org/bin/linux/ubuntu intrepid/

in my /etc/apt/sources.list file. However when I "Reload", I get the following Error message:
W: GPG error: http://cran.at.r-project.org intrepid/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D67FC6EAE2A11821

I have tried different mirror sites, but the result is the same. There is nothing written about public keys on the download of the program:
http://cran.at.r-project.org/

Then, I have tried after I added the line to the /etc/apt/sources/list file not pressing "Reload", but "Close", and I have written in the console:
sudo apt-get update
but I received similar message again:

....
Reading package lists... Done
W: GPG error: http://cran.rakanu.com intrepid/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D67FC6EAE2A11821
W: You may want to run apt-get update to correct these problems

Do you know what the problem is, and what should I do? Thanks in advance.

[spiderbatdad]

gpg --keyserver keyserver.ubuntu.com --recv D67FC6EAE2A11821
gpg --export --armor key_id | sudo apt-key add -

[gemm]

gpg --keyserver keyserver.ubuntu.com --recv D67FC6EAE2A11821
gpg --export --armor key_id | sudo apt-key add -

Thanks, it worked .

[spiderbatdad]

small mistake i trust you figured out:

gpg --keyserver keyserver.ubuntu.com --recv D67FC6EAE2A11821
gpg --export --armor D67FC6EAE2A11821 | sudo apt-key add -

[gemm]

small mistake i trust you figured out:

gpg --keyserver keyserver.ubuntu.com --recv D67FC6EAE2A11821
gpg --export --armor D67FC6EAE2A11821 | sudo apt-key add -

Yes, I have done this exactly like that, when it didn't happen with the first try .