#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

long long dp[51];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  dp[0] = 1;
  REP (i, 50) {
    dp[i+1] += dp[i];
    if (i+2 <= 50)
      dp[i+2] += dp[i];
  }
  int n;
  cin >> n;
  cout << dp[n] << endl;
  
  return 0;
}