#include<bits/stdc++.h>
#if 1 && defined(LOCAL)
    #include<LOCAL/LOCAL.hpp>
#else
    #define debug(...)
    #define line
#endif
using namespace std;
typedef long long ll;
typedef long double ld;
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return 1;}return 0;}

int N;
vector<ll>dp;
ll solve(int s){
    if(s==N-1){
        return 1;
    }
    if(dp[s]!=-1){
        return dp[s];
    }
    ll ret=0;
    if(s+1<=N-1){
        ret+=solve(s+1);
    }
    if(s+2<=N-1){
        ret+=solve(s+2);
    }
    return dp[s]=ret;
}
int main(){
    cin>>N;
    N++;
    dp.assign(N,-1);
    cout<<solve(0)<<endl;
    debug(dp);
}