import java.util.Scanner;
class Chefprac1 {
public static void main(String[] args) {
Scanner obj=new Scanner(System.in);
double bankcharge=0.50;
String data=obj.nextLine();
String []temp=data.split(" ");
double originaldata[]=new double[temp.length];
for(int i=0;i<temp.length;i++)
{
originaldata[i]=Double.parseDouble(temp[i]);
}
double amount=originaldata[0];
double accountbal=originaldata[1];
if((amount%5==0)&&(amount>0)&&(amount<=2000.00)&&(accountbal>0)&&(accountbal<2000.00)&&(amount<accountbal))
{
accountbal=accountbal-amount-bankcharge;
System.out.printf("%.2f",accountbal);
}
else
{
System.out.printf("%.2f",accountbal);
}
}
}