include <stdio.h>

int main() {

double a, c, d;
int b;
scanf("%lf", &a);
b = a + 0.999999;

if (b < 20) {

	d = b * 1.68;
}
if (b > 20) {

	c = b - 20;
	d = 20 * 1.68 + c * 1.98;
}
if (a == 20) {
	d = 20 * 1.68;
}

printf("%.2lf", d);
return 0;

}