题解 | #汽水瓶#

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    while (cin >> n)
    {
        if (n != 0)
        {
            int ans = 0;
            while (n >= 3)
            {
                ans += n / 3;
                n = n / 3 + n % 3;
            }
            if (n == 2) ++ans;
            cout << ans << endl;
        }
    }
    return 0;
}