Expectation of the median of a simple random sample

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If $(Y_1,...,Y_n)$ is a simple random sample of $Y$, a random variable with symmetric distribution such that $E[Y]=0$, how can I prove that $E[Med(Y_1,...,Y_n)]=E[Med(-Y_1,...,-Y_n)]$ (being $Med(Y_1,...,Y_n)$ the sample median)? can you give me any tip?