#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rrep(i,n) for(int (i)=((n)-1);(i)>=0;(i)--)
#define itn int
#define miele(v) min_element(v.begin(), v.end())
#define maele(v) max_element(v.begin(), v.end())
#define SUM(v) accumulate(v.begin(), v.end(), 0LL)
#define lb(a, key) lower_bound(a.begin(),a.end(),key)
#define ub(a, key) upper_bound(a.begin(),a.end(),key)
#define COUNT(a, key) count(a.begin(), a.end(), key) 
#define BITCOUNT(x) __builtin_popcount(x)
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define F first
#define S second
using P = pair <int,int>;
using WeightedGraph = vector<vector <P>>;
using UnWeightedGraph = vector<vector<int>>;
const long long INF = 1LL << 60;
const int MOD = 1000000007;
void YN(bool flg) {cout<<(flg?"YES":"NO")<<'\n';}
void Yn(bool flg) {cout<<(flg?"Yes":"No")<<'\n';}
void yn(bool flg) {cout<<(flg?"yes":"no")<<'\n';}
template <typename T> 
int getIndexOfLowerBound(vector <T> &v, T x){
    return lower_bound(v.begin(),v.end(),x)-v.begin();
}
template <typename T> 
int getIndexOfUpperBound(vector <T> &v, T x){
    return upper_bound(v.begin(),v.end(),x)-v.begin();
}
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
#define DUMPOUT cerr
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
template <typename T, typename U>
istream &operator>>(istream &is, pair<T,U> &p_var) {
    is >> p_var.first >> p_var.second;
    return is;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec) is >> x;
    return is;
}
template <typename T>
istream &operator>>(istream &is, vector<vector<T>> &df) {
    for(int i=0;i<df.size();i++)for(int j=0;j<df[i].size();j++)
    is >> df[i][j];
    return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
    DUMPOUT<<'{';
    os << pair_var.first;
    DUMPOUT<<',';
    os << " "<< pair_var.second;
    DUMPOUT<<'}';
    return os;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &vec) {
    DUMPOUT<<'[';
    for (int i = 0; i < vec.size(); i++) 
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
    DUMPOUT<<']';
    return os;
}
template <typename T>
ostream &operator<<(ostream &os, vector<vector<T>> &df) {
  for (auto& vec : df) os<<vec;
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
    DUMPOUT << "{";
    repi(itr, map_var) {
        os << *itr;
        itr++;
        if (itr != map_var.end()) DUMPOUT << ", ";
        itr--;
    }
    DUMPOUT << "}";
    return os;
}
template <typename T>
ostream &operator<<(ostream &os, set<T> &set_var) {
    DUMPOUT << "{";
    repi(itr, set_var) {
        os << *itr;
        itr++;
        if (itr != set_var.end()) DUMPOUT << ", ";
        itr--;
    }
    DUMPOUT << "}";
    return os;
}
void print() {cout << endl;}
template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail) {
  cout << head;
  if (sizeof...(tail) != 0) cout << " ";
  print(forward<Tail>(tail)...);
}
void dump_func() {DUMPOUT << '#'<<endl;}
template <typename Head, typename... Tail>
void dump_func(Head &&head, Tail &&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) > 0) DUMPOUT << ", ";
    dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \
    DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                            \
            << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]"        \
            << endl                                                            \
            << "    ",                                                         \
        dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif
template< typename T >
struct ruiseki{
    vector <T> s;
    int sz;
    ruiseki(vector <T> &a){
        sz = a.size()+1;
        s.resize(sz);
        for(int i=1;i<sz;i++) s[i] = s[i-1] + a[i-1];
    }
    T get(int a, int b){
        if(a < 0) a = 0; if(a > sz-1) a = sz-1;
        if(b > sz-1) b = sz-1;
        return s[b] - s[a];
    }
};

signed main(void) { cin.tie(0); ios::sync_with_stdio(false);
    int n; cin>>n;
    if(n %2 == 0){
        int ans = -INF;
        vector <int> a(n/2), b(n/2);
        rep(i, n) if(i%2) cin>>a[i/2]; else cin>>b[i/2];
        ruiseki <int> ra(a), rb(b);
        dump(ra.s, rb.s);
        rep(i, n/2+1){
            chmax(ans, rb.get(0, i)+ra.get(i, INF));
            dump(i, rb.get(0, i), ra.get(i, INF));
        }
        print(ans);
    }else{
        vector <int> a(n);
        cin>>a;
        vector<vector<vector<int>>> dp(2, vector<vector<int>>(5, vector<int>(n+10, -INF)));
        //使ったか使ってないか、二つ飛ばし何回やったか
        dp[1][0][0] = a[0];
        dp[0][1][0] = 0;
        for(int i=1;i<n;i++){
            rep(j, 2){
                rep(k, 3){
                    //j=0の時使わない
                    if(j == 0){
                        chmax(dp[j][k][i], dp[1][k][i-1]);
                        chmax(dp[j][k+1][i], dp[0][k][i-1]);
                    }else{//使う
                        chmax(dp[1][k][i], dp[0][k][i-1] + a[i]);
                    }
                }
            }
        }
        int ans = -INF;
        for(int i=0;i<2;i++){
            for(int j=1;j<=2;j++){
                chmax(ans, dp[i][j][n-1]);
            }
        }
        print(ans);
    }
}


Measured memory_bytes: 29864