class ATM
{
	public static void main(String[] args)
	{
		java.util.Scanner sc = new java.util.Scanner(System.in);
		double w_cash = sc.nextDouble();
		double balance = sc.nextDouble();
		if((w_cash % 5) == 0 && w_cash < balance)
		{
			double r_cash = balance - w_cash ;
			System.out.println(r_cash - 0.50);
		}
		else
		{
			System.out.println(balance);
		}

	}
}