#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <numeric>
#include <sstream>
#include <iostream>
#include <iomanip>
#define _USE_MATH_DEFINES
#include <cmath>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cfloat>
#include <cmath>
#include <ctime>
#include <cassert>
#include <cctype>
#include <cstdio>
#include <cassert>
using namespace std;

#define EPS 1e-12
#define ull unsigned long long
#define ll long long
#define VI vector<ll>
#define PII pair<ll, ll> 
#define VVI vector<vector<ll> >
#define VVVI vector<vector<vector<ll>>>
#define VVVVI vector<vector<vector<vector<ll>>>>
#define REP(i,n) for(ll i=0,_n=(n);(i)<(ll)_n;++i)
#define REPR(i,n) for(ll i=(ll)(n)-1;0<=(i);--i)
#define RANGE(i,a,b) for(ll i=(ll)a,_b=(ll)(b);(i)<_b;++i)
#define RANGER(i,a,b) for(ll i=(ll)(b)-1,_a=(ll)(a);(_a)<=i;--i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define ALLR(c) (c).rbegin(), (c).rend()
#define PB push_back
#define MP(a, b) make_pair(a, b)
#define POPCOUNT __builtin_popcount
#define POPCOUNTLL __builtin_popcountll
#define CLEAR(table, v) memset(table, v, sizeof(table));
#define UNIFORM_DOUBLE(a, b) (((b-a)*(double)rand()/RAND_MAX)+a) // [a, b) 
#define UNIFORM_LL(a, b) (ll)UNIFORM_DOUBLE(a, b) // [a, b) 
#define IN(v, lo, hi) ((lo)<=(v) && (v)<(hi))
#define DD(v) cout<<#v<<": "<<v<<endl
#define FI first
#define SE second
template <typename T0, typename T1> std::ostream& operator<<(std::ostream& os, const map<T0, T1>& v) { for( typename map<T0, T1>::const_iterator p = v.begin(); p!=v.end(); p++ ){os << p->first << ": " << p->second << " ";} return os; }
template <typename T0, typename T1> std::ostream& operator<<(std::ostream& os, const pair<T0, T1>& v) { os << v.first << ": " << v.second << " "; return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const vector<T>& v) { for( int i = 0; i < (int)v.size(); i++ ) { os << v[i] << " "; } return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const set<T>& v) { vector<T> tmp(v.begin(), v.end()); os << tmp; return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const deque<T>& v) { vector<T> tmp(v.begin(), v.end()); os << tmp; return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const vector<vector<T> >& v) { for( int i = 0; i < (int)v.size(); i++ ) { os << v[i] << endl; } return os; }
template<typename T>void maxUpdate(T& a, T b) {a = max(a, b);}
template<typename T>void minUpdate(T& a, T b) {a = min(a, b);}

#define INF (1LL<<60)

/*
N%2==0の場合
o.o.o.o.
o.o.o.Xo
o.o.Xo.o
o.Xo.o.o
Xo.o.o.o
Xは1個かつ最後使う or 0個かつ最後使わない

N%2==1の場合
o.o.o.o.X
o.o.o.Xo.
o.o.o.XXo
o.o.Xo.o.
o.o.Xo.Xo
o.o.XXo.o
o.Xo.o.o.
o.Xo.o.Xo
o.Xo.Xo.o
o.XXo.o.o
Xo.o.o.o.
Xo.o.o.Xo
Xo.o.Xo.o
Xo.Xo.o.o
XXo.o.o.o
Xは1個かつ最後使わない or 2個かつ最後使う

*/
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	ll N;
	while(cin>>N) {
		VI A(N);
		REP(i, N) cin>>A[i];
		// dp[l][s][i] 0〜iまででl=1...最後のを選んだ, s...連続して選んでない場所がs箇所
		VVVI dp(2, VVI(3, VI(N, -INF)));
		dp[0][1][0] = 0;
		dp[1][0][0] = A[0];
		RANGE(i, 1, N) REP(s, 3) {
			// 選ばない
			dp[0][s][i] = max(0<=s-1 ? dp[0][s-1][i-1] : -INF, dp[1][s][i-1]);
			// 選ぶ
			dp[1][s][i] = dp[0][s][i-1]+A[i];
		}
//		DD(dp);
		ll ans = 0;
		if(N%2==0) {
			ans = max(dp[0][0][N-1], dp[1][1][N-1]);
		} else {
			ans = max(dp[0][1][N-1], dp[1][2][N-1]);
		}
		cout<<ans<<endl;
//		break;
	}
	
	return 0;
}
/*
.XXXX
.XXXo
.XXo.
.Xo.o 2 ok
.o.Xo 2 ok
.o.o. 0 ok
o.XXX
o.XXo 3 ok
o.Xo. 1 ok
o.o.X 1 ok
o.o.o
*/



Measured memory_bytes: 19976