#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <random>
#include <set>

using namespace std;

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