#include<iostream>
using namespace std;
int main()
{
	int f(int n);
		int n;
	while(cin>>n)
	
	cout<<f(n)<<endl;
	return 0;
	
 } 
 int f(int n)
 {
 	if(n<=6)
 	return n;
 
 	else
 	return f(n-1)+f(n-3);
 }