// Problem: P1255 數樓梯
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P1255
// Memory Limit: 128 MB
// Time Limit: 1000 ms
// User: Pannnn

#include <bits/stdc++.h>

using namespace std;

vector<int> add(vector<int> a, vector<int> b) {
    vector<int> res;
    int p = 0;
    for (int i = 0; i < a.size() || i < b.size(); ++i) {
        if (i < a.size()) {
            p += a[i];
        }
        if (i < b.size()) {
            p += b[i];
        }
        res.push_back(p % 10);
        p /= 10;
    }
    if (p) {
        res.push_back(p);
    }
    return res;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n;
    cin >> n;
    vector<vector<int>> info(n + 1, vector<int>());
    info[0].push_back(1);
    info[1].push_back(1);
    for (int i = 2; i <= n; ++i) {
        info[i] = add(info[i - 1], info[i - 2]);
    }
    
    for (int i = info[n].size() - 1; i >= 0; --i) {
        cout << info[n][i];
    }
    return 0;
}