#include <bits/stdc++.h>
using namespace std;

int main() {
	double n, m = 0;
	cin >> n;
	while (n != 0) {
		int d = n + 0.999999;
		if (d <= 4)
			m = 10;
		else if (d > 4 && d <= 8)
			m = 10 + (d - 4) * 2;
		else {
			int x = d / 8;
			m = 18 * x;
			d %= 8;
			if (d <= 5)
				m += d * 2.4;
			else
				m += (10 + (d - 4) * 2);
		}
		if (m == floor(m))
			printf("%.0lf\n", m);
		else
			printf("%.1lf\n", m);
		scanf("%lf", &n);
	}
	return 0;
}