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

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