A word of advice, gleaned from piping-fresh first-hand experience.
If you have the opportunity to do any travel by bus in Peru, and you're assigned to seats 1, 2, 3 or 4... ask very nicely whether you might be able to change your seat assignment. It doesn't much matter where, just do yourself a favour and request a higher seat number.
Why, you ask?
Peruvian driving is... how shall I put this? Insane and scary as hell. And if you're in the front row on the top level of a double-decker bus, you get to see the insanity up close and personal. "Safe following distance?" HA! Yield the right of way to pedestrians? HA HA! It is to laugh. Double-yellow means no passing? Thank you for that quaint... suggestion.
So unless you're looking for hours of nail-biting, seat-gripping, laughing-in-the-face-of-certain-death fun... move to the back of the bus.