#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
using ll = long long;
const int INF = 1e9;
#define put(n) cout<<(n)<<endl
#define rep(i,N) for(int(i)=0;(i)<(N);++(i))
#define rrep(i,N) for(int (i)=(N-1);(i)>=(0);--(i))
#define all(v) (v).begin() , (v).end()
#define rall(v) (v).rbegin() , (v).rend()
#define pb(n) push_back(n)

ll dp[55];

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

    cout << dp[N] << endl;
    
}