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

#define rep(i, n) for( int i = 0; i < n; i++ )
using ll = long long;

int main() {
	ll N;
	cin >> N;
	if(N <= 3) {
		cout << 1 << endl;
		return 0;
	}
	N -= 3;
	ll l = 0, h = 2e9;
	while(h - l > 1) {
		ll m = (l + h) / 2;
		ll f = m * 5 + m * (m - 1);
		if(N <= f) h = m;
		else l = m;
	}
	cout << h + 1 << endl;
}