#include <iostream>

using namespace std;

int main()
{
    int n;
    cin >> n;

    int x = 0;
    while (n > 2)
    {
        x++;
        n = n - 3;
    }
    cout << x << endl;

    return 0;
}
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;
using ll = long long;
using P = pair<int, int>;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(), v.end()
#define sz(x) ((int) x.size())
#define pb push_back
#define mp make_pair
#define F first
#define S second
typedef vector<ll> vi;
const int MOD = 1000000007;
template<class T> void print(const T& t){ cout << t << endl; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

int main(){
  ll n;
  cin >> n;
  print(n / 3);
}