#include <iostream>
#include <vector>
using namespace std;
using vi = vector<int>;

#define rep(i,n) for(int i=0,_i=(n);i<_i;++i)

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

  vector<long long> dp(N+2, 0);
  dp[0] = 1;
  rep(i, N) {
    dp[i+1] += dp[i]; dp[i+2] += dp[i];
  }
  cout << dp[N] << endl;
  return 0;
}