In PROBLEM F,1311F Can anybody explain at what point below coordinates coincide?

3
1 5 10
9 6 1

A B C (suppose names of points)

Ans is 0 I guess. But I don't understand at which point? (maybe I'm assuming something wrong)

At 1 sec: A = 10, B = 11, C = 11 (Only d(B,C)=0)

At 1.x sec:

A = 11.a, C = 11.a, B = 11.b where b>a ( only d(A,C)=0)

At 1.y sec: (y>x)

C = 11.c, A = 11.d, B = 11.d where b>a (only d(A,B)=0)

At 1.z sec: (z>y)

C = e, B = f, A = g where g>f>e (diff increases more hereafter)