#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <random>
#include <iomanip>
#include <unordered_set>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int
// #define endl '\n';
#define fi first
#define se second
#define NONVOID [[nodiscard]]
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
template<class T> inline void dump(T &v){irep(i, v){cout<<*i<<((i==--v.end())?'\n':' ');}}
inline string getline(){string s; getline(cin,s); return s;}
inline void yn(const bool b){b?fin("yes"):fin("no");}
inline void Yn(const bool b){b?fin("Yes"):fin("No");}
inline void YN(const bool b){b?fin("YES"):fin("NO");}
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;
const double EPS = 1e-9;



int main() {
    
    ll n;
    cin>>n;
    vll v(n),maxNum(n);
    ll num=1,maxK=3;
    

    rep(i,n){
        scanf("%lld",&v[i]);
    }
    rep(i,n){
        if(i==maxK){
            num++;
            maxK+=2;
        }
        maxNum[i]=num;
    }
    
    vector<map<ll,ll>> dp(n,map<ll,ll>());
    for(int i=0;i<n;i++){
        dp[i][1]=v[i];
        for(int k=2;k<=4;k++){ //-4,-3,-2
            if(i-k<0)continue;
            for(auto l=dp[i-k].begin();l!=dp[i-k].end();l++){// kの場所のたて
                ll Val=l->second+v[i];
                ll kosu=l->first+1;
                if(kosu<maxNum[i]){
                    continue;
                } else {
                    if(dp[i].count(kosu)==1)chmax(dp[i][kosu],Val);
                    else dp[i][kosu]=Val;
                }
            }
        }
    }
    ll ans=-LLINF;
    for(int i=0;i<n;i++){
        irep(j,dp[i]){
            if(j->first==n/2){
                chmax(ans,j->second);
            }
        }
    }
    fin(ans);
    // rep (i,n)cout<<i<<" "<<dp[i].size()<<endl;
    // irep(i,dp[2])cout<<i->fi<<" "<<i->se<<endl;
    // dump(maxNum);
}


/*
7
-1 -2 -3 -4 -5 -6 -7
0
1 -3
2 0
*/

Measured memory_bytes: 47144