TH-TMO 2011 Problem 6

For any $0\leq x_1,x_2,\ldots,x_{2011} \leq 1$ , Find the maximum value of \begin{align*} \sum_{k=1}^{2011}(x_k-m)^2 \end{align*} where $m$ is the arithmetic mean of $x_1,x_2,\ldots,x_{2011}$ .