n1 = int(input())
n2 = int(input())
i = 2
x0 = (n1**2 + n2**2)/i
x = ((n1 + n2)/i)**2
while n2 != 0:
    sigma = ((x0 - x)*(i/(i - 1)))**(0.5)
    n2 = int(input())
    i += 1
    x0 = (x0*(i-1) + n2**2) / i
    x = ((((x)**(0.5))*(i - 1) + n2)/i)**2
print(sigma)