include <stdio.h>

int main() { int x; float a;

scanf("%d", &x);
scanf("%f", &a);

if(0< x <=2000 && 0<= a <= 2000) {
    if(x%5 == 0) {
            a = a - x-0.50;
        }
}
printf("%.2f", a);

return 0;

}