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

signed main(){
  int N; cin >> N;
  vector< long long > dp( N + 1 );
  dp[ 0 ] = 1;
  for( int i = 0; i < N; ++i ){
    if( i + 1 <= N )
      dp[ i + 1 ] += dp[ i ];
    if( i + 2 <= N )
      dp[ i + 2 ] += dp[ i ];
  }
  cout << dp[ N ] << endl;
  return 0;
}