include <stdio.h>

int main() {

double a, b, d;
scanf("%lf", &b);
int c;
c = b + 0.999999999;

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

}