#include <iostream>
#include <vector>
#include<string>
#include<algorithm>
using namespace std;

int dp[1005] = {0};
int floor(int n){
	dp[1] = 1;
	dp[2] = 2;
	dp[3] = 4;
	for(int i = 4; i<=n; i++){
		dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
	}
	return dp[n];
}

int main(){
	int n;
	while(cin>>n){
		int res = floor(n);
		cout<<res<<endl;	
	}
	return 0;
}