How to ssh in to default ec2 created by docker-machine?

I’m having trouble connecting to my ec2 generated by docker-machine via ssh. Here is the code I ran:

docker-machine create -d amazonec2 --amazonec2-region=us-east-1 example

I tried using all the .pem files located in ~/.docker/machine/machines/example

ssh -i key.pem ec2-user@[ip-address]

The documentation for docker-machines and docker-cloud could definitely be a lot better.