n=input()
arr=map(float,raw_input().split())
if n==2:
        print (arr[0]+arr[1])/2
else:
        arr.sort()
        tot=arr[0]+arr[1]
        c=2
        for i in range(2,n):
                tot+=c*arr[i]
                c*=2
        print tot/pow(2,n-1)
