include <stdio.h>

int main() { double x, y; int d; scanf("%lf", &x); if (x <= 15) {

y = 4 * x / 3;
printf("%.2lf", y);

} if (x > 15) {

y = 2.5 * x - 10.5;
printf("%.2lf", y);

} return 0; }