#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int grupos = n / 3;
  int residuo = n % 3;
  int regalos = grupos * 2;
  if (residuo != 0) {
    regalos = regalos + 1;
  }
  cout << regalos << endl;
  return 0;
}
