Hello,

I was following these instructions: https://www.monetdb.org/downloads/deb/

I think there is a mistake in the page and the command

sudo wget --output-document=/etc/apt/trusted.gpg.d/monetdb.gpg /downloads/MonetDB-GPG-KEY.gpg

should be replaced with  

sudo wget --output-document=/etc/apt/trusted.gpg.d/monetdb.gpg https://www.monetdb.org/downloads/MonetDB-GPG-KEY.gpg