Unit disk/n points/Exists point with distance at least n/Exercise

Let $n$ points $P_1,P_2,\dots ,P_n$ in the unit disk $B$ be given, that is, $B=\{P\in {ℝ}^2\mid d(P,0)\le 1\}$. Show that there exists a point $Q\in B$ fulfilling the property

$\sum _{i=1}^{n}d(P_i,Q)\ge n.$

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