#include <bits/stdc++.h>
using namespace std;
int ans[1001];
int main() {
  int n;
  cin >> n;
  if (n == 1 or n == 2)
    cout << "1" << endl;
  else if (n % 3 == 0)
    cout << (n / 3) + (n / 3) << endl;
  else
    cout << (n / 3) + (n / 3) + 1 << endl;
  return 0;
}
