#include<stdio.h>
int main()
{
int x;
float y;
scanf("%d",&x);
scanf("%f",&y);
if(x>0&&x<=2000)
{
if(x%5==0)
{
if(y>x)
{
if(y>=0&&y<=2000)
{
printf("%0.2f",y=y-x-0.5);
}
else
{
printf("%f",y);
}
}
else
{
printf("%0.2f",y);
}
}
else
{
printf("%0.2f",y);
}
}
else
{
printf("0.2%f",y);
}
return 0;
}