import java.util.*;
import java.io.*;
class Main
{
public static void main
(String args
[]) {
Scanner sc
=new Scanner
(System.
in); float balance,withdraw,cbalance;
withdraw=sc.nextInt();
balance=sc.nextInt();
if(withdraw%5==0)
{
cbalance=(balance-withdraw)-0.50f;
if(cbalance<0)
System.
out.
format("%.2f%n",balance
); else
System.
out.
format("%.2f%n",cbalance
); }
else
{
}
}
}
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