#include
#include
using namespace std;
int main() {
// your code goes here
int x;
cin>>x;
double y;
cin>>y;
if(x%5==0){
double left=y-x-0.50;
if(left>0){
cout<<fixed<<setprecision(2)<<left<<endl;
}else{
cout<<fixed<<setprecision(2)<<y<<endl;
}
}else{
cout<<fixed<<setprecision(2)<<y<<endl;
}
return 0;
}