#include <iostream>
#include <cstring>
using namespace std;

typedef long long ll;
const int maxn = 105;
const double EPS = 1e-7;
int n;
ll dp[100];
ll rec(int at) {
    if(at >= n) {
        return 1;
    }
    if(dp[at] != -1) {
        return dp[at];
    }
    ll res = 0;
    res += rec(at + 1);

    for(int j = at + 3; j <= n; j++) {
        res += rec(j + 1);
    }
    return dp[at] = res;
}
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n;
    memset(dp, -1, sizeof dp);
    cout << rec(0) << endl;
    return 0;
}