// Problem : F - Select Half
// Contest : AtCoder Beginner Contest 162
// URL : https://atcoder.jp/contests/abc162/tasks/abc162_f
// Memory Limit : 1024 MB
// Time Limit : 2000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define D(x) cerr << #x << " is " << (x) << "\n";
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define D(x) cerr << #x << " is " << (x) << "\n";
#define ld long double
#define li __int128

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<class T1, class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1, class T2> istream& operator>>(istream& is,pair<T1,T2>& a) {is>>a.f>>a.s;return is;}
template<class T> istream& operator>>(istream& is,vector<T>& a) {for(auto &p:a)is>>p;return is;}
//istream& operator>>(istream& is,__int128& a){string s;is>>s;a=0;for(auto p:s)a=a*10+p-'0';return is;}
//ostream& operator<<(ostream& os,__int128 a){bool neg=false;if(a<0)neg=true,a*=-1;ll high=(a/(__int128)1e18);ll low=(a-(__int128)1e18*high);string res;if(neg)res+='-';if(high>0){res+=to_string(high);string temp=to_string(low);res+=string(18-temp.size(),'0');res+=temp;}else res+=to_string(low);os<<res;return os;}

const int N=2e5+5;
const ll oo=LLONG_MIN/2;
ll dp[N][3];
int n;
vector<int> a;
ll calc(int tr,int k){
	if(tr>=n){
		if(k==0)
			return 0;
		return oo;
	}
	if(dp[tr][k]!=oo)
		return dp[tr][k];
	if(k)
		dp[tr][k]=max(dp[tr][k],calc(tr+1,k-1));
	dp[tr][k]=max(dp[tr][k],calc(tr+2,k)+a[tr]);
	return dp[tr][k];
}
int main()
{
	for(int i=0;i<N;i++)
		dp[i][0]=dp[i][1]=dp[i][2]=oo;
	scanf("%i",&n);
	a.resize(n);
	for(int i=0;i<n;i++)
		scanf("%i",&a[i]);
	n++;
	a.pb(oo);
	ll ans;
	if(n%2==1)
		ans=calc(0,1);
	else
		ans=calc(0,2);
	printf("%lld\n",ans);
	return 0;
}


Measured memory_bytes: 13472