UVa 11150 - Cola

// UVa 11150 - Cola

#include <iostream>
using namespace std;

int main() {
	int n;
	while (cin >> n) {
		int full = n;
		int empty = 2;
		int drank = 0;
		while (true) {
			if (full) {
				empty += full;
				drank += full;
				full = 0;
			} else {
				int pos_full = empty / 3;
				int pos_empty = empty % 3;
				if (pos_full + pos_empty < 2 && pos_full > 0) {
					pos_full--;
					pos_empty += 3;
				}
				if (full == pos_full && empty == pos_empty)
					break;
				else {
					full = pos_full;
					empty = pos_empty;
				}
			}
		}
		cout << drank << endl;
	}
	return 0;
}