// No.44 DPなすごろく
// https://yukicoder.me/problems/no/44
//
#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;

long long int solve(unsigned int N);


int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    unsigned int N;
    cin >> N;

    long long ans = solve(N);
    cout << ans << endl;
}

long long int solve(unsigned int N) {
    vector<vector<long long>> dp;
    dp.resize(N+1);
    for (auto y = 0; y< N+1; ++y)
        dp[y].resize(N+1);
    dp[0][0] = 1;

    for (auto i = 1; i <= N; ++i) {
        for (auto j = i; j <= N; ++j) {
            long long t = 0;
            for (auto k = 1; k <= 2; ++k) {
                if (j - k < 0)
                    continue;
                t += dp[i-1][j-k];
            }
            dp[i][j] = t;
        }
    }

    long long total = 0;
    for (auto i = 0; i <= N; ++i)
        total += dp[i][N];
    return total;
}