# C - Alchemist

n = int(input())
v = list(map(int, input().split()))
v.sort()

while len(v) > 2:
    pre = v[1] - v[0]
    nxt = v[2] - v[1]
    if pre < nxt:
        v[0] = (v[1] + v[0]) / 2
    else:
        v[2] = (v[2] + v[1]) / 2
    v.pop(1)
print((v[0] + v[1]) / 2)