import java.util.*;
public class Main {
public static void main (String[] args) {
Scanner sc = new Scanner (System.in);
int X = sc.nextInt();
double Y = sc.nextInt();
if(X % 5 == 0 && X < Y) {
double q = Y - X - .50;
System.out.printf("%.2f\n",q);
}
else if((X % 5 == 0) && (X > Y)) {
System.out.printf("%.2f\n",Y);
}
else {
System.out.printf("%.2f\n",Y);
}
}
}