RU-ALLRUSSIAN 1973 Problem 14

a, b, c, d, e are positive reals. Show that $(\mathrm{a} + \mathrm{b} + \mathrm{c} + \mathrm{d} + \mathrm{e})^2\geq 4(\mathrm{ab} + \mathrm{bc} + \mathrm{cd} + \mathrm{de} + \mathrm{ea})$