Debian Rcmdr misses sem leaps etc

Hello,when I start up Rcmdr under Jessie Debian I get the message that there are packages missing:sem, markdown, leaps, knitr, aplpackIt then wants to get these from cran. But first I have to tell where to put them: I HAVE NO IDEA.I downloaded Rcmdr via a package program.Can anyone help me to get a good Rcmdr?with friendly greetings,Peter