#include<iostream>

using namespace std;

long long s[75];

int main() {
	
	s[0] = 1, s[1] = 1, s[2] = 2;
	
	for (int i = 3; i <= 70; i ++) {
		s[i] = s[i - 1] + s[i - 2] + s[i - 3];
	}
	
	int x;
	while (cin >> x) {
		cout << s[x] << endl;
	}
	
	return 0;
}