include

using namespace std; double b, ans; int a;

int main() {

cin >> b;
a = b;
if (b > a)
	a++;
if (a <= 20)
	ans = a * 1.68;
else
	ans = 20 * 1.68 + (a - 20) * 1.98;
printf("%.2lf", ans);
return 0;

}