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 > 0 && w_cash <= 2000) && (balance >= 0 && balance <= 2000)) {

			if((w_cash % 5) == 0 && w_cash < balance) {
				double r_cash = balance - w_cash ;
				System.out.println(r_cash - 0.50);
			}
			else if(w_cash >= balance || (w_cash % 5) != 0) {
				System.out.println(balance);
			}
		}
	}
}