#include <stdio.h>
#include <iostream>
#include <string.h>
using namespace std;
int a[1010];
int main()
{
	int n;
	cin >> n;
	int sum = n;
	int cnt = 0;
	int f = 1;
	for(int i = 1 ; i >= 1 && i <= n ; i += f)
	{
		if(a[i] == 0)
		{
			cnt++;
			if(sum == 2)
			{
				cout << i << endl;
				break;
			}
			if(cnt%3 == 0)
			{
				sum--;
				a[i] = 1;
			}
		}
		if( (i == 1 && f == -1) || (i == n && f == 1) )
		{
			cnt = 0;
			if(a[i]==0)
				cnt = 1;
			f = -f;
		}
	}
}