include <stdio.h>

int main() {

int a;
double b;
scanf("%d", &a);
if (a < 5) {
	b = a * 20;
}
if (a >= 5 && a < 10) {
	b = a * 20 * 0.9;
}
if (a >= 10) {
	b = a * 20 * 0.8;
}
printf("%.2lf", b);
return 0;

}