#include <stdio.h>
int main(void)
{
int draw;
float total, remain;
scanf("%d%f", &draw, &total);
if (draw % 5 == 0 && (draw > 0 && draw < total))
{
remain = total - (draw + 0.50);
printf("%0.2f\n", remain);
}
else
{
printf("%0.2f\n", total);
}
return 0;
}