include

using namespace std;

int main() {

double a, b, c;
int d;
scanf("%lf", &a);
d = a + 0.99999;
if (d <= 20) {
	c = d * 1.68;
	printf("%.2lf", c);
}
if (d > 20) {
	b = (d - 20) * 1.98 + 20 * 1.68;
	printf("%.2lf", b);
}

return 0;

}