import java.io.;
import java.util.;
class atm
{
public static void main(String args[])throws IOException
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String s=br.readLine();String s1="";int x=0;
for(int i=0;i<s.length();i++)
{ char ch=s.charAt(i);
if(ch==’ ')
{ x=Integer.parseInt(s1);
s1="";
}
else s1=s1+ch;
}
double y=Double.parseDouble(s1);
if(x>2000||y>2000)System.exit(0);
if((x%5)!=0)
{System.out.println(y);
System.exit(0);}
double amount=y-(double)x-0.5;
if(amount>=0)
System.out.println(amount);
else
System.out.println(y);
}
}