#include <bits/stdc++.h>
using namespace std;
int main(){
	vector<long long> dp(71);
	dp[0] = 1;
	dp[1] = 1;
	dp[2] = 2;
	for(int i=3;i<71;i++){
		dp[i] = dp[i-1]+dp[i-2]+dp[i-3];
	}
	int n;
	while(cin>>n){
		cout<<dp[n]<<endl;
	}
	return 0;
}