How to find the username of the instance launched in amazon-ec2

Question

I m having trouble connecting to the amazon ec2 instance using ssh. The key pair matches and I know that the username is not the same for all instances. 

How can I find the username of the instance that I have launched?

I am getting this error:

Permission denied (public key).

on trying this:

ssh -i test-instance.pem  ec2-user@23.22.214.148

Any help will be appreciated.