#include <algorithm>
#include <cstdint>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, s, t) for (int i = s; i < t; i++)
#define ALL(obj) obj.begin(), obj.end()

const int iINF = 1e9;
const long long llINF = 1e18;
const int MOD = 1e9 + 7;
template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}

template <int MOD>
struct ModInt {
    long long val;
    constexpr ModInt(long long v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr ModInt operator-() const noexcept { return val ? MOD - val : 0; }
    constexpr ModInt operator+(const ModInt& r) const noexcept { return ModInt(*this) += r; }
    constexpr ModInt operator-(const ModInt& r) const noexcept { return ModInt(*this) -= r; }
    constexpr ModInt operator*(const ModInt& r) const noexcept { return ModInt(*this) *= r; }
    constexpr ModInt operator/(const ModInt& r) const noexcept { return ModInt(*this) /= r; }
    constexpr ModInt& operator+=(const ModInt& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr ModInt& operator-=(const ModInt& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr ModInt& operator*=(const ModInt& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr ModInt& operator/=(const ModInt& r) noexcept {
        long long a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b;
            swap(a, b);
            u -= t * v;
            swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator==(const ModInt& r) const noexcept { return this->val == r.val; }
    constexpr bool operator!=(const ModInt& r) const noexcept { return this->val != r.val; }
    friend constexpr ostream& operator<<(ostream& os, const ModInt<MOD>& x) noexcept { return os << x.val; }

    friend constexpr istream& operator>>(istream& is, ModInt<MOD>& x) noexcept { return is >> x.val; }
    friend constexpr ModInt<MOD> modpow(const ModInt<MOD>& a, long long n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};

using mint = ModInt<MOD>;

long long modPow(long long x, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * x % mod;
        x = x * x % mod;
        n >>= 1;
    }
    return res;
}

long long extGCD(long long a, long long b, long long& x, long long& y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }

    long long d = extGCD(b, a % b, y, x);
    y -= a / b * x;
    return d;
}

long long gcd(long long a, long long b) {
    if (b == 0) {
        return a;
    } else {
        return gcd(b, a % b);
    }
}

long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }

const int MAX = 300000;
template <typename T>
map<T, int> compress(vector<T> x) {
    map<T, int> res;
    sort(x.begin(), x.end());
    x.erase(unique(x.begin(), x.end()), x.end());
    for (int i = 0; i < x.size(); i++) {
        res[x[i]] = i;
    }

    return res;
}

vector<long long> fac(MAX + 1), inverseFac(MAX + 1);

long long modPow(long long x, long long n) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * x % MOD;
        x = x * x % MOD;
        n >>= 1;
    }
    return res;
}

long long comb(long long a, long long b) {
    if (a == 0 && b == 0) return 1;
    if (a < b || a < 0) return 0;
    long long tmp = inverseFac[a - b] * inverseFac[b] % MOD;
    return tmp * fac[a] % MOD;
}

long long perm(long long a, long long b) {
    if (a < b) return 0;
    long long tmp = inverseFac[a - b] % MOD;
    return tmp * fac[a] % MOD;
}

long long dupc(long long a, long long b) {
    if (a == 0 && b == 0) return 1;
    if (a < 0 || b == 0) return 0;
    long long tmp = inverseFac[a - 1] * inverseFac[b] % MOD;
    return tmp * fac[a + b - 1] % MOD;
}

void init() {
    fac[0] = 1;
    inverseFac[0] = 1;
    for (long long i = 0; i < MAX; i++) {
        fac[i + 1] = fac[i] * (i + 1) % MOD;
        inverseFac[i + 1] = inverseFac[i] * modPow(i + 1, MOD - 2) % MOD;
    }
}

template <typename T>
using Vec = vector<T>;
template <typename T>
using VVec = vector<vector<T>>;
using LL = long long;
int main() {
    int N;
    cin >> N;
    Vec<int> A(N);
    REP(i, N) cin >> A[i];
    const int skip = 1 + N % 2;
    VVec<LL> dp(N + 2, Vec<LL> (skip + 1, -llINF));
    dp[0][0] = 0;
    REP(i, N + 1) {
        REP(j, skip + 1) {
            if (j < skip) chmax(dp[i + 1][j + 1], dp[i][j]);
            if (i < N) chmax(dp[i + 2][j], dp[i][j] + A[i]);
        }
    }
    cout << dp[N + 1][skip] << endl;
    return 0;
}

Measured memory_bytes: 19632