#!/usr/bin/env python3
import sys
import calc_library

list =  sys.stdin.read()
s = 0
total = 0
total_sqr = 0
text = list.split()
N = len(text)
first = calc_library.div(1, calc_library.sub(N,1))
for i in text:
    number = float(i)
    total = calc_library.add(total, number)
    total_sqr =calc_library.add(total_sqr, calc_library.power(number, 2))
x = calc_library.div(total, N)
s = calc_library.sqr(calc_library.mul(first,calc_library.sub(total_sqr, calc_library.mul(N, calc_library.power(x, 2)))),2)
print(s)