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#define _CRT_SECURE_NO_DEPRECATE

#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>

#define ull unsigned long long
#define ll long long

using namespace std;

const int N = 81;
const ll INF = 1000ll * 1000 * 1000 * 1000 * 1000 * 1000ll;

ll a[N];
ll d[N];


int main() {
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	int n;
	cin >> n;
	for (int i = 0; i <= n; i++) {
		d[i] = 0ll;
	}
	d[0] = d[1] = 0;
	d[2] = d[3] = 1;
	for (int i = 4; i <= n; i++) {
		d[i] = d[i - 2] + d[i - 3];
	}
	cout << d[n];

	return 0;
}