Are you allowed to go to heaven if you don’t believe in god?

So I am not a very religious person and this is a question I have always wondered. What does the Bible say about this?

What I don’t get is let’s say there is a guy John Doe 1 who kills multiple people and is a terrible person but asks for forgiveness and repents he earns a ticket to heaven. And there is another guy John Doe 2 who is a great person his whole life but doesn’t believe in god, and he earns a ticket to hell. Seems unfair