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

int main() { 
	long long dp[70];
	dp[0] = 1;
	dp[1] = 1;
    dp[2] = 2;
	for (int i = 3; i <= 70; i++) {
    	dp[i] = (dp[i-1] + dp[i-2]+ dp[i-3]);
    }
	int n;
    while (cin >> n) {       
        cout << dp[n] << endl;
    }
    return 0;
}