#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

ll dp[55];

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