512
root: *noder1 *noder2 *noder3 *noder4 
noder1: *noder1 *q1grad *q1grad *noder1
q1grad: 0 *q1grad *q1grad 1
noder2: *q2grad *noder2 *noder2 *q2grad
q2grad: *q2grad 0 1 *q2grad
noder3: *q3grad *noder3 *noder3 *q3grad
q3grad: *q3grad 1 0 *q3grad
noder4: *noder4 *q4grad *q4grad *noder4
q4grad: 1 *q4grad *q4grad 0