import java.util.*;
import java.io.*;
class atm
{
{
double w,c;
Scanner input
=new Scanner
(System.
in); w=input.nextDouble();
c=input.nextDouble();
double ans = 0.0;
if ( w%5==0 && c>=(w+0.5) )
c = c - w - 0.5;
//else if(w%5==0 && w>=c)
// ans = c;
//else if(w%5!=0 || w>=c)
// ans = c;
}
}
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