I Center of inversion of cubic diamond structure?

[IcedCoffee]

I'm having hard time finding the center of inversion of cubic diamond structure.

At first I thought (2,2,2) would be the center of inversion, but (1,1,3), (3,3,3), (1,3,1), (3,1,1) (i.e. four atoms inside the cube) are not centrosymmetric about (2,2,2).

 

[IcedCoffee]

Ah, I see. It's on a midpoint between two atoms like (2.5, 1.5, 0.5)...