Generalized Gr\"unbaum inequality

Let $f$ be an integrable log-concave function on ${\mathbb R^n}$ with the center of mass at the origin. We show that $\int\limits_0^{\infty}f(s\theta)ds\ge e^{-n}\int\limits_{-\infty}^{\infty}f(s\theta)ds$ for every $\theta\in S^{n-1}$, and the constant $e^{-n}$ is the best possible.