/*
    Author:zeke
    
    pass System Test!
    GET AC!!
*/
#include <iostream>
#include <queue>
#include <vector>
#include <iostream>
#include <vector>
#include <string>
#include <cassert>
#include <algorithm>
#include <functional>
#include <cmath>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <map>
#include <iomanip>
#include <utility>
#include <stack>
#include <bitset>
using ll = long long;
using ld = long double;
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define rep3(var, min, max) for (ll(var) = (min); (var) < (max); ++(var))
#define repi3(var, min, max) for (ll(var) = (max)-1; (var) + 1 > (min); --(var))
#define Mp(a, b) make_pair((a), (b))
#define F first
#define S second
#define Icin(s) \
    ll(s);      \
    cin >> (s);
#define Scin(s) \
    ll(s);      \
    cin >> (s);
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;
}
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef vector<V> VV;
typedef vector<P> VP;
ll mod = 1e9 + 7;
ll MOD = 1e9 + 7;
ll INF = 1e18;
const int N = pow(10, 5);

vector<bool> isp(N + 1, true);

long long modMult(long long a, long long b, long long m)
{
    long long res = 0;
    long long exp = a % m;
    while (b)
    {
        if (b & 1)
        {
            res += exp;
            if (res > m)
                res -= m;
        }
        exp <<= 1;
        if (exp > m)
            exp -= m;
        b >>= 1;
    }
    return res;
}
long long powMod(long long a, long long b, long long m)
{
    long long res = 1;
    long long exp = a % m;
    while (b)
    {
        if (b & 1)
            res = modMult(res, exp, m);
        exp = modMult(exp, exp, m);
        b >>= 1;
    }
    return res;
}
//powMod(a,b,MOD)
//O(log(b))?
int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll n;
    cin >> n;
    V vec(n);
    rep(i, n) cin >> vec[i];
    if (n % 2 == 0)
    {
        ll even=0, odd=0;
        rep(i, n)
        {
            if (i % 2 == 0)
            {
                even += vec[i];
            }
            else
            {
                odd += vec[i];
            }
        }
        cout << max(even, odd) << endl;
        return 0;
    }
    ll dp[n + 1][2][2];
    rep(i, n + 1) rep(j, 2) rep(k, 2) dp[i][j][k] = -1e18;
    dp[0][0][0]=0;
    rep(i, n)
    {
        chmax(dp[i+1][0][1],dp[i][0][0]);
        chmax(dp[i+1][1][1],dp[i][0][1]+vec[i]);
        chmax(dp[i+1][1][0],dp[i][0][0]+vec[i]);
        chmax(dp[i+1][0][1],dp[i][1][1]);
        chmax(dp[i+1][0][0],dp[i][1][0]);
        cout<<dp[i+1][0][0]<<" "<<dp[i+1][1][0]<<" "<<dp[i+1][0][1]<<" "<<dp[i+1][1][1]<<endl;
    }
    cout << max(dp[n][1][1],dp[n][0][1]) << endl;
}
