#include <iostream>
#include <utility>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <functional>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
using namespace std;
using ll = long long int;
#define chmax(x,y)  x = (x > (y)) ? x : (x = (y));
#define chmin(x,y)  x = (x < (y)) ? x : (x = (y));


int main(int argc, char const *argv[])
{
  int N; cin >> N;
  vector<ll> dp(N+1,0);
  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];
  }
  std::cout << dp[N] << std::endl;
}