Need help

I am trying to learn the Crosby Stills Nash and Young song Helplessly Hoping, but I am having trouble with the chord progression. Every tab i can find has the first measure as Am, but it just doesn't fit. Maybe I am playing it wrong, but the only way it sounds right to me is with Am7. The notes inside aside, if anyone has eather confermation for my Am7 theory of insight into how to play it with Am i would appreciate it. thanks