/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author Gosu_Hiroo
 */

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#ifdef int
#define VI vector<long long>
#define V2I(v,size_1, size_2, value) vector<vector<long long>>v(size_1, vector<long long>(size_2, value))
#define V3I(v,size_1,size_2,size_3,value) vector<vector<vector<long long>>>v(size_1,vector<vector<long long>>(size_2,vector<long long>(size_3, value)))
#define G(g,size_1) vector<vector<long long>>g(size_1, vector<long long>())
#define SZ(x) ((long long)(x).size())
#define READ ({long long t;cin >> t;t;})
#define PII pair<long long, long long>
#else
#define VI vector<int>
#define V2I(v,size_1, size_2, value) vector<vector<int>>v(size_1, vector<int>(size_2, value))
#define V3I(v,size_1,size_2,size_3,value) vector<vector<vector<int>>>v(size_1,vector<vector<int>>(size_2,vector<int>(size_3, value)))
#define G(g,size_1) vector<vector<int>>g(size_1, vector<int>())
#define SZ(x) ((int)(x).size())
#define READ ({int t;cin >> t;t;})
#define PII pair<int, int>
#endif

#define V2(v,type,size_1, size_2, value) vector<vector<type>>v(size_1, vector<type>(size_2, value))
#define V3(v,type,size_1,size_2,size_3,value) vector<vector<vector<type>>>v(size_1,vector<vector<type>>(size_2,vector<type>(size_3, value)))

#define TR(container, it) \
        for (auto it = container.begin(); it != container.end(); it++)
#define IN(c, x) ((c).find(x) != (c).end())   //O(log n)
#define IN_L(c, x) (find((c).begin(),(c).end(),x) != (c).end()) //O(n)
#define FOR(i, _begin, _end) for (__typeof(_end) end = _end, begin = _begin,  i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define REP(i, end) for (__typeof(end) i = 0, _len = (end); i < (_len); i += 1)
#define ALL(x) (x).begin(),(x).end()
#define F first
#define S second
#define y0 y3487465
#define y1 y8687969
#define j0 j1347829
#define j1 j234892
#define MOD(x, m) ((((x) % (m)) + (m)) % (m))
#define BIT(n) (1LL<<(n))
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define EB emplace_back
#define PB push_back
#define fcout cout << fixed << setprecision(12)
#define fcerr cerr << fixed << setprecision(12)
#define print(x) cout << (x) << endl
#define fprint(x) cout << fixed << setprecision(12) << (x) << endl
# define BYE(a) do { cout << (a) << endl; return ; } while (false)

#ifdef DEBUG
#define ERR(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); _err(cerr,_it, args); }
#define DBG(x) cerr << #x << " is " << x << endl;
#else
#define DBG(x) {};
#define ERR(args...) {};
#endif
void _err(std::ostream& cerr,istream_iterator<string> it) {cerr << endl;}
template<typename T, typename... Args>
void _err(std::ostream& cerr, istream_iterator<string> it, T a, Args... args) {
    cerr << *it << " = " << a << "  ";
    _err(cerr,++it, args...);
}

const double pi = 2 * acos(.0);
const int inf = 0x3f3f3f3f;
const ll mod = (ll) (1e9) + 7;
//const ll mod = (ll) 998244353 ;
const double eps = 1e-10;

template<typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
    std::fill((T *) array, (T *) (array + N), val);
}

template <typename T>
istream& operator >> (istream& is, vector<T>& V) {
    for(auto&& ele : V)is >> ele;
    return is;
}

template <typename T>
ostream& operator << (ostream& os, const vector<T> V) {
    os << "[";
    int cnt = 0;
    T curr;
    if(!V.empty()){
        for (int i = 0; i < V.size() - 1; ++i) {
            if(V[i] == curr)cnt ++;
            else cnt = 0;
            if(cnt == 4)os << "... ";
            if(cnt < 4)
                os << V[i] << " ";
            curr = V[i];
        }
        os << V.back();
    }
    os << "]";
    return os;
}

template <typename T, typename U>
ostream& operator << (ostream& os, const pair<T,U> P) {
    os << "(";
    os << P.first << "," << P.second;
    os << ")";
    return os;
}

template <typename T, typename U>
ostream& operator << (ostream& os, const set<T,U> V) {
    os << "{";
    if(!V.empty()){
        auto it = V.begin();
        for (int i = 0; i < V.size() -1; ++i) {
            os << *it << " ";
            it++;
        }
        os << *it;
    }
    os << "}";
    return os;
}

template <typename K, typename H, typename P>
ostream& operator << (ostream& os, const unordered_set<K, H, P> V) {
    os << "{";
    if(!V.empty()){
        auto it = V.begin();
        for (int i = 0; i < V.size() -1; ++i) {
            os << *it << " ";
            it++;
        }
        os << *it;
    }
    os << "}";
    return os;
}

template <typename K, typename C>
ostream& operator << (ostream& os, const multiset<K, C> V) {
    os << "{";
    if(!V.empty()){
        auto it = V.begin();
        for (int i = 0; i < V.size() -1; ++i) {
            os << *it << " ";
            it++;
        }
        os << *it;
    }
    os << "}";
    return os;
}

template <typename K, typename T, typename C>
ostream& operator << (ostream& os, const map<K,T,C> V) {
    os << "{";
    if(!V.empty()){
        auto it = V.begin();
        for (int i = 0; i < V.size() -1; ++i) {
            os << "(";
            os << it->first << "," << it->second;
            os << ") ";
            it++;
        }
        os << "(";
        os << it->first << "," << it->second;
        os << ")";
    }
    os << "}";
    return os;
}

template <typename K, typename T, typename C>
ostream& operator << (ostream& os, const unordered_map<K,T,C> V) {
    os << "{";
    if(!V.empty()){
        auto it = V.begin();
        for (int i = 0; i < V.size() -1; ++i) {
            os << "(";
            os << it->first << "," << it->second;
            os << ") ";
            it++;
        }
        os << "(";
        os << it->first << "," << it->second;
        os << ")";
    }
    os << "}";
    return os;
}

template <typename T>
ostream& operator << (ostream& os, const deque<T> V) {
    os << "[";
    if (!V.empty()) {
        for (int i = 0; i < V.size() - 1; ++i) {
            os << V[i] << "->";
        }
        if (!V.empty())os << V.back();
    }
    os << "]";
    return os;
};

template <typename T, typename Cont, typename Comp>
ostream& operator << (ostream& os, const priority_queue<T, Cont, Comp> V) {
    priority_queue<T, Cont, Comp> _V = V;
    os << "[";
    if(!_V.empty()){
        while(_V.size() > 1){
            os << _V.top() << "->";
            _V.pop();
        }
        os << _V.top();
    }
    os << "]";
    return os;
};

template <class F>
struct y_combinator {
    F f; // the lambda will be stored here

    // a forwarding operator():
    template <class... Args>
    decltype(auto) operator()(Args&&... args) const {
        // we pass ourselves to f, then the arguments.
        // the lambda should take the first argument as `auto&& recurse` or similar.
        return f(*this, std::forward<Args>(args)...);
    }
};
// helper function that deduces the type of the lambda:
template <class F>
y_combinator<std::decay_t<F>> recursive(F&& f){
return {std::forward<F>(f)};
}

struct hash_pair {
    template <class T1, class T2>
    size_t operator()(const pair<T1, T2>& p) const
    {
        auto hash1 = hash<T1>{}(p.first);
        auto hash2 = hash<T2>{}(p.second);
        return hash1 ^ hash2;
    }

};

template<class T>void Chmod(T &a, const T &m) {a = MOD(a, m);}
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; }
//256MB = 2^29(~5.3*10^8)*sizeof(int)
#define int ll //2^31=2.15*10^9, 2^63=9.22*10^18
template< typename Monoid >
struct SegmentTree {
    using F = function< Monoid(Monoid, Monoid) >;

    int sz;
    vector< Monoid > seg;

    const F f;
    const Monoid M1;

    SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
        sz = 1;
        while(sz < n) sz <<= 1;
        seg.assign(2 * sz, M1);
    }

    void set(int k, const Monoid &x) {
        seg[k + sz] = x;
    }

    void build() {
        for(int k = sz - 1; k > 0; k--) {
            seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
        }
    }

    void update(int k, const Monoid &x) {
        k += sz;
        seg[k] = x;
        while(k >>= 1) {
            seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
        }
    }

    Monoid query(int a, int b) {
        Monoid L = M1, R = M1;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
            if(a & 1) L = f(L, seg[a++]);
            if(b & 1) R = f(seg[--b], R);
        }
        return f(L, R);
    }

    Monoid operator[](const int &k) const {
        return seg[k + sz];
    }

    template< typename C >
    int find_subtree(int a, const C &check, Monoid &M, bool type) {
        while(a < sz) {
            Monoid nxt = type ? f(seg[2 * a + type], M) : f(M, seg[2 * a + type]);
            if(check(nxt)) a = 2 * a + type;
            else M = nxt, a = 2 * a + 1 - type;
        }
        return a - sz;
    }


    template< typename C >
    int find_first(int a, const C &check) {
        Monoid L = M1;
        if(a <= 0) {
            if(check(f(L, seg[1]))) return find_subtree(1, check, L, false);
            return -1;
        }
        int b = sz;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
            if(a & 1) {
                Monoid nxt = f(L, seg[a]);
                if(check(nxt)) return find_subtree(a, check, L, false);
                L = nxt;
                ++a;
            }
        }
        return -1;
    }

    template< typename C >
    int find_last(int b, const C &check) {
        Monoid R = M1;
        if(b >= sz) {
            if(check(f(seg[1], R))) return find_subtree(1, check, R, true);
            return -1;
        }
        int a = sz;
        for(b += sz; a < b; a >>= 1, b >>= 1) {
            if(b & 1) {
                Monoid nxt = f(seg[--b], R);
                if(check(nxt)) return find_subtree(b, check, R, true);
                R = nxt;
            }
        }
        return -1;
    }
};
class FSelectHalf {
public:

void solve(std::istream& cin, std::ostream& cout, std::ostream& cerr) {
    int N;
    cin >> N;
    VI a(N), s_l(N/2+2), s_r(N/2+2);
    cin >> a;
    REP(i,N)if(i%2==0)s_l[i/2+1] = s_l[i/2] + a[i];else s_r[i/2+1] = s_r[i/2] + a[i];
    ERR(s_l, s_r)
    SegmentTree<ll> seg(N, [](ll a, ll b){return max(a,b);}, -1e18);
    REP(i,N/2+1)seg.update(i, s_l[i] - s_r[i]);
    if(N%2==0)print(s_r[N/2] + seg.query(0, N/2+1));
    else{
        auto dp = recursive([&](auto &&dp, int ind)->ll{
            ll res = -1e18;
            if(ind == 3)return max(max(a[0], a[1]), a[2]);
            ERR(ind, s_r[ind/2] + seg.query(0, ind/2+1))
            Chmax(res, s_r[ind/2] + seg.query(0, ind/2+1));
            Chmax(res,dp(ind-2) + a[ind-1]);
            ERR(ind, res)
            return res;
        });
        print(dp(N));
    }



}


};


#undef int
int main() {

	FSelectHalf solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
    std::ostringstream err;
	in.tie(0); ios::sync_with_stdio(0);
    solver.solve(in, out,err);
	return 0;
}


Measured memory_bytes: 26236