/*input
1
1

*/
 
/*
                                                    ______________
                                                          |       )
                                                          |   )   /
                                                          |______/
                                                    |     |      \
                                                    |     |   )   \
                                                    |_____|_______)
 
*/
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <ctime>
#include <cassert>
#include <complex>
#include <string>
#include <cstring>
#include <chrono>
#include <random>
#include <queue>
#include <bitset>
#include <iomanip>
#include <fstream>
#include <stack>

using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef pair<ll , ll> PLL;
typedef long double ld;
 
#define pb push_back
#define all(c) c.begin(),c.end()
#define allr(c) c.rbegin(),c.rend()
int mod = 1000000007;
const int inf = 1034567891;
const ll LL_INF = 1234567890123456789ll;
#define PI 3.14159265
#define endl '\n'
#define F first
#define S second
#define debug(x) cout << #x << " = " << x << endl;
#define TRACE
 
#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
  cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
  const char* comma = strchr(names + 1, ',');cout.write(names, comma - names) << " : " << arg1<<" | ";__f(comma+1, args...);
}
#else
#define trace(...)
#endif
 
#define out(container) for (auto it : container) cout << it << " "; cout << endl;
 
 
template < typename T > T GCD(T a, T b)            { ll t; while(a) { t = a; a = b % a; b = t; } return b; }
template < typename T > string toString(T a)       { return to_string(a); }
template < typename T > void toInt(string s, T &x) { stringstream str(s); str >> x;}
inline int add(int x, int y){ x += y; if(x >= mod) x -= mod; return x;}
inline int sub(int x, int y){ x -= y; if(x < 0) x += mod; return x;}
inline int mul(int x, int y){ return (x * 1ll * y) % mod;}
inline int powr(int a, ll b){
  int x = 1 % mod;
  while(b){
    if(b & 1) x = mul(x, a);
    a = mul(a, a);
    b >>= 1;
  }
  return x;
}
inline int inv(int a){ return powr(a, mod - 2);}

int n;
vector<int> vec;
vector<int> arr;
map<string, ll> mp;

ll fun(int ind, int need, int prev) {
  if (ind == n) {
    // if (need) return -inf;
    return 0ll;
  }
  string str = to_string(ind) + "|" + to_string(need) + "|" + to_string(prev);
  if (mp.find(str) != mp.end()) return mp[str];
  int can = (n - ind) / 2;
  ll ans = -LL_INF;
  if (ind == 0) {
    // arr.pb(vec[ind]);
    ans = max(ans, vec[ind] + fun(ind + 1, need - 1, ind));
    // arr.pop_back();
    ans = max(ans, fun(ind + 1, need, prev));
  }
  if (can >= need) {
    if (ind - 1 != prev && need) {
      // arr.pb(vec[ind]);
      ans = max(ans, vec[ind] + fun(ind + 1, need - 1, ind));
      // arr.pop_back();
    }
    ans = max(ans, fun(ind + 1, need, prev));
  } else {
    if (ind - 1 != prev && need) {
      // arr.pb(vec[ind]);
      ans = max(ans, vec[ind] + fun(ind + 1, need - 1, ind));
      // arr.pop_back();
    }
  }
  return mp[str] = ans;
}

int main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  
  cin >> n;
  ll v;
  for (int i = 0; i < n; i++) {
    cin >> v;
    vec.pb(v);
  }
  ll ans = fun(0, n / 2, -1);
  cout << ans << endl;

  return 0;
}

Measured memory_bytes: 169860