#include<iostream>
using namespace std;

typedef long long ll;

const int N=80;

int n;
ll fib[N];

int main()
{
	fib[0]=1,fib[1]=1,fib[2]=2;
	for(int i=3;i<N;i++)
		fib[i]=fib[i-1]+fib[i-2]+fib[i-3];
	while(cin>>n)
		cout<<fib[n]<<endl;
	return 0;
}