#include <bits/stdc++.h>
using namespace std;
#define int long long
// #define LL long long
#define endl '\n'

int n;

void solve()
{
	cin >> n;
	int drink = 0;
	int cnt = 0;
	while (n > 0)
	{
		n--, drink++; // 每开一瓶，就喝下一瓶
		cnt++; // 总共喝的数量+1
		if (drink == 3) // 喝了三瓶
		{
			n++; // 三个瓶盖换一瓶
			drink = 0;
		}
	}
	cout << cnt << endl;
}

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);

	solve();

	return 0;
}