x0 = 0
x1 = x0
x2 = x1
x3 = x2
x4 = x3
x5 = x4
x6 = x5
x7 = x6
x8 = x7
x9 = x8
x10 = x9
x11 = x10
x12 = x11
x13 = x12
x14 = x13