lab2-3

from math import sqrt
p1 = float(input())
p2 = float(input())
p3 = float(input())
avg = (p1 + p2 + p3) / 3
res = sqrt( ((p1 - avg) ** 2 + (p2 - avg) ** 2 + (p3 - avg) ** 2) / 6)
print(res)

"""
from math import sqrt
q = float(input())
res = sqrt(q ** 2 + 0.1 ** 2)
print(res)
"""
"""
from math import sqrt
p1avg = 12.87
p2avg = 12.9
d1 = 0.1
d2 = 0.1
pavg = 12.89
res = pavg * sqrt(0.25 * d1 ** 2 / p1avg ** 2 + 0.25 * d2 ** 2 / p2avg ** 2)
print(res)
"""