#include <bits/stdc++.h>
using namespace std;
using lli = long long;
using ld = long double;
mt19937 rnd(time(nullptr));
inline void Solve() {
  int n = 0;
  cin >> n;
  int ans = n / 3 * 2 + (n % 3 != 0);
  cout << ans;
}
signed main() {
  cout << fixed << setprecision(20);
  Solve();
  return 0;
}
