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

int main() {
    int n; cin >> n;
    vector<ll> dp(n + 1, 0);
    dp[0] = dp[1] = 1;
    for (int i = 2; i <= n; i++) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    cout << dp[n] << endl;
    return 0;
}