#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
using ll = long long;

int main() {
    int n; cin >> n;
    vector<ll> dp(n + 2, 0);
    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;
}