Certbot not found

i installed letsencrypt on my ubuntu 16.04 machine with following command. ``` sudo apt-get install letsencrypt ``` Now, i want to define a cronjob to automatically renew my certs with following line. ``` certbot renew --pre-hook "service nginx stop" --post-hook "service nginx start" ``` But i always get the error, that the command certbot could not be found. If i use letsencrypt instead of certbot everything works fine as long as i dont use the `--pre-hook` and `--post-hook`. How to install `certbot`or is there an alternative command for letsencrypt to define such hooks? Thanks