#include <bits/stdc++.h>
using namespace std;

#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);
using ll = long long;

int main() {
  FAST;
  
  int tc = 1, ti;
  // cin >> tc;

  for (ti = 1; ti <= tc; ++ti) {
    int n, ans;
    cin >> n;

    ans = 0;
    while (n % 3 != 0) {
      n -= 2;
      ans += 1;
    }
    ans += n/3;

    cout << ans << "\n";
  }

  return 0;
}