#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
typedef long long ll;

int main(){
	vector<int> v(1001);
	int cnt=0;
	for(int i=1; i<1002; i++){
		if(i%3==0) cnt++;
		v[i]=cnt;
	}
	int n; cin>>n;
	cout<<v[n]<<endl;
}
#include <bits/stdc++.h>

using namespace std;
 
using ll = long long;
using ull = unsigned long long;
using ldouble = long double;
 
const ll inf = 1ll << 60;
const ll mod = (ll)1e9 + 7;

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define print(s) cout << s;
#define println(s) cout << s << endl;
#define printd(s) cout << fixed << setprecision(10) << s << endl;

string res;

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

    println(n / 3);

}
