#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std; // NOLINT

int main() {
    int32_t n;
    cin >> n;
    vector<int64_t> dp(n + 1);
    dp[0] = 1;
    for (auto i = 1; i <= n; ++i) {
        int64_t t = 0;
        if (i - 1 >= 0)
            t += dp[i - 1];
        if (i - 2 >= 0)
            t += dp[i - 2];
        dp[i] = t;
    }
    cout << dp[n] << endl;
    return 0;
}