a[999],n,i;main(j){for(scanf("%d",&n);~scanf("%d",a+i++);)for(j=i;--j&&a[j-1]>a[j];)a[j-1]^=a[j]^=a[j-1]^=a[j];i=!printf("%f",(a[n/2]+a[~-n/2])*.5);}