#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using P = pair<int, int>;

const int INF = 1e9;
const int MOD = 1e9 + 7;

int main() {
  int N;
  cin >> N;

  ll dp[N+1];
  dp[1] = 1;
  dp[2] = 2;
  for (int i = 3; i <= N; i++) {
    dp[i] = dp[i-1] + dp[i-2];
  }

  cout << dp[N] << endl;
  return 0;
}