#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 f[51];

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

  f[0] = f[1] = 1;
  for (int i = 2; i <= 50; i++) {
    f[i] = f[i-1] + f[i-2];
  }

  int n;
  cin >> n;
  cout << f[n] << endl;
  
  return 0;
}