# statistical distance in symmetric-key encryption

Prove that for any symmetric-key encrytion scheme $$\Pi=(Gen, Enc, Dec)$$ with message space $$M$$ and key space $$K$$, there exist $$m_0, m_1 \in M$$ such that $$\Delta(Enc(K, m_0), Enc(K, m_1))\ge 1-\frac{|K|}{|M|}$$.

I know that $$\Delta(X,Y)=\max\limits_{T\subseteq S}(Pr(X\in T)-Pr(Y\in T))$$, but I have no idea about the inequation above. I tried to prove by contradiction but failed.