# -*- coding: utf-8 -*-

s = list(map(int,input().split()))

s.sort()

del s[0]
del s[-1]
sum = 0

for i in range(len(s)):
    sum += s[i]

if sum % 4 == 0:
    st = str(sum/4) + "0"
else:
    st = str(round(sum/4,2))

print(st)