#include<bits/stdc++.h>
using namespace std;
int f(int i){
    if(i==3) return 4;
    if(i==2) return 2;
    if(i==1) return 1;
    else return f(i-1)+f(i-2)+f(i-3);
}
int main(){
    int n;
    cin>>n;
    cout<<f(n+1);
}
/**************************************************************
	Problem: 1689
	User: chenlingxuan
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/