Monge-Ampère Equation with Bounded Periodic Data

We consider the Monge-Amp\`ere equation $\det(D^2u)=f$ in $\mathbb{R}^n$, where $f$ is a positive bounded periodic function. prove that $u$ must be sum of quadratic polynomial and For $f\equiv 1$, this classic result by J\"orgens, Calabi Pogorelov. $f\in C^\alpha$, was proved Caffarelli first named author.