include <stdio.h>

include <math.h>

int main() {

double n, c;
int b;

scanf("%lf", &n);
b=ceil(n);
if (b <= 20) {
	c = 1.68 * b;
}else{
	c=20*1.68+(b-20)*1.98;
}

printf("%.2lf", c);

return 0;

}