Env. Variables not set while running Minimal Flask application

Question

I am trying to follow the flask documentation on my windows machine given at the following link: http://flask.pocoo.org/docs/0.11/quickstart/#debug-mode

Firstly I wrote

Answer 1

Just drop the space around '=' !

After half an hour searching for solution, I finally get what does 'You did not provide the FLASK_APP environment variable' mean. Because what I set is 'FLASK_APP ' variable (with space).