#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, c = 0, t = 0, l = 1;
  cin >> n;
  while (n > 0) {
    swap(t, l);
    if (t == 1) {
      if (n - 1 >= 0) {
        n--;
      } else {
        break;
      }
    } else if (t == 0) {
      if (n - 2 >= 0) {
        n -= 2;
      } else {
        break;
      }
    }
    c++;
  }
  cout << c;
}
