#include <iostream>
#include <queue>
#include <vector>
#include <cmath>
#include <algorithm>
#include <map>
#include <numeric>

using namespace std;
using ll = long long;
const ll INF = 1e9;
const ll MOD = 1e9 + 7;

ll dp[52];

int main() {
    int N;
    cin >> N;

    dp[0] = 1;
    for (int i = 0; i < N; i++) {
        dp[i+1] += dp[i];
        dp[i+2] += dp[i];
    }

    cout << dp[N] << endl;

    return 0;
}