#include <iostream>
#include <vector>
using namespace std;

int main(void) {
  int N; cin >> N;
  vector<unsigned long long> pat(N + 1);
  pat[0] = 1;
  pat[1] = 1;
  for (int i = 2; i <= N; i++) pat[i] = pat[i-1] + pat[i-2];
  cout << pat[N] << endl;
  return 0;
}