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

S.sort()

ans = sum(S[1:-1])

print(ans // 4, end='')

if ans % 4 == 0:
    
    print('.00')
    
elif ans % 4 == 1:
    
    print('.25')
    
elif ans % 4 == 2:
    
    print('.50')
    
else:
    
    print('.75')