l=length
j _ _[]=""
j r t(x:s)=([1..t-d]>>" ")++x++"\n"++j(mod(r+1)2) u s where(d,u)=last$(l x,t-l x):[(0,t+l x)|r==0]
main=interact(j 0 0.zipWith($)(cycle[id,reverse]).words)