lawl
I just failed...
NAND + NOT = AND
but now I know what to do. I make these 4 outputs (the 2 calculations), 2 of them go in CACLULATOR 3, and 2 go in CACLULATOR 4. The 20 and 22 get sent to the end. The 21 output (both of them) get sent to an NIMPLIES gate (negated IMPLIES (IMPLIES + NOT)), and that calculation is the final 21 calculation. Yay!
And that fails too... The NIMPLIES needs to be just an OR.
The problem is... you need to walk west, and start from the furthest lever away, and turn them on in succesion going back east. If you don't, the OR gate will do some wierd things with your number, like say 0 + 0 + 1 + 0 (in the order described above) = 10.
There isn't much of a problem to this, as who in their right mind, if they wanted to calculate, would turn on 2 randomly chosen ones, rather than two next to each other on the end they started at.