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

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