#include <bits/stdc++.h>
using namespace std;

int n,i,j,dp[4][40000];
 
int main() {
	int n;
	cin>>n;
	
	for(int i = 1;i <= 3;i++){
		dp[i][0] = 1;//初始化 
		//j从i开始循环，防止背包容量不够 
		for(int j = 1;j <= n;j++){
			if(j < i){
				dp[i][j] = dp[i - 1][j];
			} else{
				dp[i][j] = dp[i - 1][j] + dp[i][j - i]; 	
			}
		}
	}
	
	cout<<dp[3][n];
	return 0;
}
/**************************************************************
	Problem: 1885
	User: admin
	Language: C++
	Result: Accepted
	Time:19 ms
	Memory:2700 kb
****************************************************************/