RU-ALLRUSSIAN 1979 Problem 10

$\mathbf{x}_{\mathrm{i}}$ are real numbers between 0 and 1. Show that $\left(\mathbf{x}_{1} + \mathbf{x}_{2} + \ldots +\mathbf{x}_{\mathrm{n}} + 1\right)^{2}\geq 4(\mathbf{x}_{1}^{2} + \mathbf{x}_{2}^{2} + \ldots +\mathbf{x}_{\mathrm{n}}^{2})$ .