#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  vector<int64_t> A(N + 10, 0);
  A[0] = 1;
  for (int i = 0; i < N; i++) {
    A[i + 1] += A[i];
    A[i + 2] += A[i];
  }
  cout << A[N] << '\n';
  return 0;
}