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;
}