#include <bits/stdc++.h>
#include <atcoder/all>


using namespace std;
using namespace atcoder;
#define rep(i,m,n,k) for (int i = (int)(m); i < (int)(n); i += (int)(k))
#define rrep(i,m,n,k) for (int i = (int)(m); i > (int)(n); i += (int)(k))
#define ll long long
#define list(T,A,N) vector<T> A(N);for(int i=0;i<(int)(N);i++){cin >> A[i];}


int main(){
    
    ll N;
    cin >> N ;
    vector<ll> A(N+5,0);
    A[0] = 1;
    rep(i,0,N,1){
        A[i+2] += A[i];
        A[i+1] += A[i];
    };
    cout << A[N] << endl;
    return 0;


}