#include <iostream>
using namespace std;
int main() {
	int n;
	long long a[71];
	while (cin >> n) {
		for (int i = 0; i <= n; i++) {
			if (i == 0 || i == 1) {
				a[i] = 1;
				continue;
			}
			if (i == 2) {
				a[i] = 2;
				continue;
			}
			a[i] = a[i - 1] + a[i - 2] + a[i - 3];
		}
		cout << a[n] << endl;
	}
	return 0;
}