import sys
input=lambda: sys.stdin.readline().rstrip()
A=sorted([int(i) for i in input().split()])
ans=sum(A[1:5])
if ans%4==0:
  print(str(ans//4)+".00")
if ans%4==1:
  print(str(ans//4)+".25")
if ans%4==2:
  print(str(ans//4)+".50")
if ans%4==3:
  print(str(ans//4)+".75")