# ATM

 import sys

 withdraw, balance = map(float, sys.stdin.readline().strip().split())  # strip()用法去除结尾的\n符号

 if int(withdraw) % 5 != 0 or balance < (withdraw + 0.5):  # 1.注意手续费,缺少手续费也不能取 2.xy0~2000是测试值要求，不用判断

     print("%.2f" % balance)

 else:

     print("%.2f" % (balance - withdraw - 0.5))