include <stdio.h>

int main() {

double a, b, c, n;
int d;
scanf("%lf", &a);
d = a + 0.99999;
if (20 >= d) {
	c = d * 1.68;

}
if (d > 20) {
	c = (d - 20) * 1.98 + 20 * 1.68;
}
printf("%.2lf", c);
return 0;

}