#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define mp make_pair
#define REP(m,n) for(ll i=m;i<n;i++)
#define REPj(m,n) for(ll j=m;j<n;j++)
#define MOD 1000000007
#define INF 10000000000000000

int main(){
	vector<int>v;
	int n;
	cin>>n;
	REP(0,n){
		int tmp;
		cin>>tmp;
		if(i<2){
			v.push_back(tmp);
		}else{
			if(i==2){
				v.push_back(v[0]+tmp);
			}else{
				v.push_back(max(v[i-2],v[i-3])+tmp);
			}
		}
	}
	int ans;
	if(n==1){
		ans=v[n-1];
	}else{
		ans=max(v[n-1],v[n-2]);
	}	
	cout<<ans<<endl;
}