#include
#include
using namespace std;
int main()
{
float x,y;
int z;
z=x;
cin>>x>>y;
if (( 0 < x <= 2000)&&( 0<= y <= 2000)&&(y-(x+0.05)>=0))
{
if(z%5==0)
{
y=y-(x+0.5);
cout<<setprecision(2)<<fixed;
cout<<y;
}
else
{
cout<<setprecision(2)<<fixed;
cout<<y;
}
}
else
{
cout<<setprecision(2)<<fixed;
cout<<y;
}
}