#include <bits/stdc++.h>

using namespace std;

#define llong long long int
#define ldouble long double
#define fore(i, x) for (auto &i : n)
#define rep(i, n) for (int i = 0; i < n; ++i)
#define repr(i, n) for (int i = n; i >= 0; --i)
#define stl_rep(itr, x) for (auto itr = x.begin(); itr != x.end(); ++itr)
#define all(x) x.begin(), x.end()
#define allr(x) x.rbegin(), x.rend()

const static int mod = 1000000000 + 7;
const static int inf = INT_MAX / 2;
const static llong INF = LLONG_MAX / 2;
const static double eps = 1e-6;
const static int dx[] = {1, 0, -1, 0};
const static int dy[] = {0, 1, 0, -1};

template<class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1;} return 0;}

template<class T> bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1;} return 0;}

signed main (int argc, char *argv[]) {
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int n;
    cin >> n;
    llong dp[51];
    dp[0] = 1;
    for (int i = 1; i <= n; ++i) {
        if (i == 1) {
            dp[i] = dp[i - 1];
        } else {
            dp[i] = dp[i - 1] + dp[i - 2];
        }
    }

    cout << dp[n] << endl;
    return 0;
}