#include<iostream>
using namespace std;

int main(){
	int n;
	int ans =0;
	int i = 4;
	int check[3] = { 1, 2, 4 };

	cin >> n;

	switch (n){
	case 1:
		ans = 1;
		break;
	case 2:
		ans = 2;
		break;
	case 3:
		ans = 4;
		break;
	default :
		while (n >= i){
			ans = check[0] + check[1] + check[2];
			i++;
			check[0] = check[1];
			check[1] = check[2];
			check[2] = ans;
		}
	}

	cout << ans << endl;

	return 0;
}