#include <bits/stdc++.h>

using namespace std;

vector< vector< pair <long long, long long> > > dp;

const long long INF = 1e18;
pair <long long, long long> operator +(pair <long long, long long> a,pair <long long, long long> b)
{
    pair <long long, long long> res = {a.first + b.first, a.second + b.second};
    if (res.second >= INF)
    {
        res.second -= INF;
        ++res.first;
    }

    return res;
}

void print(pair<long long, long long> res)
{
    if (res.first == 0)
        cout << res.second;
    else
    {
        string s = "";
        for (int i = 0; i < 18; ++i, res.second /= 10)
            s += char('0' + (res.second % 10));

        reverse(s.begin(), s.end());

        cout << res.first << s;
    }
}


int main()
{
//    freopen("j.in", "r", stdin);
    int n;
    cin >> n;

    dp.resize(n, vector< pair <long long, long long> >(2, {0, 0}));

    dp[0][0] = {0, 1};
    dp[0][1] = {0, 1};

    for (int i = 1; i < n; ++i)
        dp[i][0] = dp[i - 1][0] + dp[i - 1][1], dp[i][1] = dp[i - 1][0];

    pair<long long, long long> res = dp[n - 1][0] + dp[n - 1][1];

    print(res);

    return 0;
}