#include <bits/stdc++.h>

using namespace std;

#define rep(i, n) for(int i = 0; i < (int)n; ++i)
#define FOR(i, a, b) for(int i = a; i < (int)b; ++i)
#define rrep(i, n) for(int i = ((int)n - 1); i >= 0; --i)

typedef long long ll;
typedef long double ld;

const int Inf = 1e9;
const double EPS = 1e-9;
const int MOD = 1e9 + 7;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(0);
    int n;
    cin >> n;
    vector<ll> dp(n + 3);
    dp[0] = 1;
    rep (i, n + 1) {
        FOR (j, 1, 3) {
            if (dp[i]) dp[i + j] += dp[i];
        }
    }
    cout << dp[n] << endl;
    
    return 0;
}