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

int main() {
  long N;
  cin >> N;
  vector<long> DP(N + 2);
  DP.at(0) = 1;
  for (long i = 0; i < N; i++) {
    DP.at(i + 1) += DP.at(i);
    DP.at(i + 2) += DP.at(i);
  }
  cout << DP.at(N) << "\n";
}