#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
#define MP make_pair
#define rep(i,j) for(int (i) = 0; (i) < (j); ++(i))
#define int long long

signed main(){
   int N; cin>>N;
   int dp[60];
   dp[0] = dp[1] = 1;
   for(int i=2;i<=N;++i) dp[i] = dp[i-1] + dp[i-2];
   cout<<dp[N]<<endl;
}