5

def der(p, n):
    res = [0]*(n-1)
    for i in range(n - 1):
        res[i] = p[i] * (n - i - 1)
    return res


def value(p, x):
    n = len(p)
    val = 0
    for i in range(n):
        val += (x ** (n - i - 1)) * p[i]
    return val


def solution(n, p):
    x0 = 1
    eps = 1e-6
    max_iters = 1e6
    x, x_prev, i = x0, x0 + 2*eps, 0
    if value(p, x0) == 0:
        return x0
    while abs(x - x_prev) >= eps and i < max_iters:
        x, x_prev, i = x - value(p, x) / value(der(p, n+1), x), x , i + 1
    return x


n = int(input())
print(solution(n, [float(i) for i in input().split()]))