Steps taken:


Ideal:
4

0
x1y1
a1b1
x1y2
a1b2
x1y3
a1b3
x1y4
a1b4
x2y1
a2b1
x2y2
a2b2
x2y3
a2b3
x2y4
a2b4
x3y1
a3b1
x3y2
a3b2
x3y3
a3b3
x3y4
a3b4
x4y1
a4b1
x4y2
a4b2
x4y3
a4b3
x4y4
a4b4

Beijing, China