N = int(input())
V = [int(x) for x in input().split()]

V.reverse()

ans = []

for i in range (1, len(V)):
    if i == 1:
        prev = i-1
        res = (V[prev] + V[i]) / 2
    else:
        res = (prev + V[i]) / 2

    ans.append(res)
    prev = res

print(ans[-1])
