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

#define rep(i,s,n) for (int i = (int)s; i < (int)n; i++)
#define ll long long
#define ld long double
#define pb push_back
#define eb emplace_back
#define All(x) x.begin(), x.end()
#define Range(x, i, j) x.begin() + i, x.begin() + j
#define lbidx(x, y) lower_bound(x.begin(), x.end(), y) - x.begin()
#define ubidx(x, y) upper_bound(x.begin(), x.end(), y) - x.begin()
#define llbidx(x, y, z) lower_bound(x.begin(), x.end(), z) - lower_bound(x.begin(), x.end(), y) // 二要素間の距離
#define deg2rad(deg) ((((double)deg)/((double)360)*2*M_PI))
#define rad2deg(rad) ((((double)rad)/(double)2/M_PI)*(double)360)
#define Find(set, element) set.find(element) != set.end()
#define Decimal(x) printf("%.10f\n", x) // 小数点を10桁まで表示
// debug用
#define PrintVec(x) for (auto elementPrintVec: x) { cout << elementPrintVec << " "; } cout << "\n";
#define debug(x) cerr << #x << ": " << (x) << "\n";
#define endl "\n"
// gcj print用
#define Case(x) printf("Case #%d: ", x);

typedef pair<int, int> PI;
typedef pair<ll, ll> PLL;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<vector<int>>> vvvi;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef vector<vector<vector<int>>> vvvl;
typedef vector<PI> vpi;
typedef vector<vector<PI>> vvpi;
typedef vector<vector<vector<PI>>> vvvpi;
typedef vector<PLL> vpl;
typedef vector<vector<PLL>> vvpl;
typedef vector<vector<vector<PLL>>> vvvpl;

int POWINT(int x, int n) {
  int ret = 1;
  while (n > 0) {
    if (n & 1) ret *= x;
    x *= x;
    n >>= 1;
  }
  return ret;
};

ll POWLL(ll x, int n) {
  ll ret = 1;
  while (n > 0) {
    if (n & 1) ret *= x;
    x *= x;
    n >>= 1;
  }
  return ret;
};

template<class T>
inline bool chmax(T &a, T b) {
  if(a < b) {
    a = b;
    return true;
  }
  return false;
};

template<class T>
inline bool chmin(T &a, T b) {
  if(a > b) {
    a = b;
    return true;
  }
  return false;
};

ll dp[200010][3];
const ll INF = 1ll << 60;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int N;
  cin >> N;
  vl A(N);
  rep(i, 0, N) {
    cin >> A[i];
  }

  if (N % 2 == 0) {
    dp[N-1][2] = A[N-1];
    dp[N-2][2] = A[N-2];
    for (int i = N-3; i >= 0; i--) {
      if (i % 2 == 1) {
        dp[i][0] = A[i] + max(max(dp[i+2][0], dp[i+2][1]), max(dp[i+3][2], dp[i+4][2]));
        dp[i][1] = max(dp[i+1][2], dp[i+2][2]);
        dp[i][2] = A[i] + dp[i+2][2];
      } else {
        dp[i][0] = A[i] + max(max(max(dp[i+2][0], dp[i+2][1]), max(dp[i+3][0], dp[i+3][1])), max(dp[i+4][2], dp[i+5][2]));
        dp[i][1] = max(max(dp[i+1][0], dp[i+1][1]), max(dp[i+2][2], dp[i+3][2]));
        dp[i][2] = A[i] + max(dp[i+2][2], dp[i+3][2]);
      }
    }
    ll ans = max(dp[0][2], dp[1][2]);
    cout << ans << endl;
  } else {
    dp[N-1][2] = A[N-1];
    dp[N-2][2] = A[N-2];
    for (int i = N-3; i >= 0; i--) {
      if (i % 2 == 0) {
        dp[i][0] = A[i] + max(max(dp[i+2][0], dp[i+2][1]), max(dp[i+3][2], dp[i+4][2]));
        dp[i][1] = max(dp[i+1][2], dp[i+2][2]);
        dp[i][2] = A[i] + dp[i+2][2];
      } else {
        dp[i][0] = A[i] + max(max(max(dp[i+2][0], dp[i+2][1]), max(dp[i+3][0], dp[i+3][1])), max(dp[i+4][2], dp[i+5][2]));
        dp[i][1] = max(max(dp[i+1][0], dp[i+1][1]), max(dp[i+2][2], dp[i+3][2]));
        dp[i][2] = A[i] + max(dp[i+2][2], dp[i+3][2]);
      }
    }
    ll ans = max(max(dp[0][0], dp[0][1]), max(dp[1][2], dp[2][2]));
    cout << ans << endl;
  }



  return 0;
};


Measured memory_bytes: 9532