/* package codechef; // don’t place package name! */
import java.util.*;
import java.text.*;
import java.lang.*;
import java.io.*;
/* Name of the class has to be “Main” only if the class is public. */
class Codechef
{
public static void main (String[] args) throws java.lang.Exception
{
Scanner ans=new Scanner(System.in);
DecimalFormat np=new DecimalFormat("#.00");
float n,y;
n=ans.nextFloat();
y=ans.nextFloat();
if(n>0 && n<=2000 && y>=0 && y<=2000)
{
if(n<y)
{
if(n%5==0)
{
y=(float)(y-n-0.5);
}
}
}
System.out.println(np.format(y));
}
}
/*what is the one condition which I missed to take while solving the problem */