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

using int64 = long long;

template<typename T>
using p_que = priority_queue<T>;
template<typename T>
using rp_que = priority_queue<T, vector<T>, greater<T>>;

constexpr int INF = (1 << 30) - 1;
constexpr int64 INF64 = (1ll << 60) - 1;

#define rep(i, N) for(int i=0;i<(int)(N);++i)
#define fs first
#define sc second
#define e_b emplace_back
#define m_p make_pair
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()

template <typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
	return os << "P(" << p.first << ", " << p.second << ")";
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
	os << "[";
	for (auto& e : v) os << e << ", ";
	return os << "]";
}
template <typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& m) {
	os << "{" << endl;
	for (auto& e : m) os << "(" << e.first << ", " << e.second << ")" << endl;
	return os << "}";
}
template <typename T>
ostream& operator<<(ostream& os, const set<T>& s) {
	os << "{" << endl;
	for (auto& e : s) os << ", " << e << endl;
	return os << "}";
}

template<typename T>
vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts>
auto make_v(size_t a, Ts... ts) {
	return vector<decltype(make_v(ts...))>(a, make_v(ts...));
}

int64 gcd(int64 x, int64 y) {
	if (x == 0 || y == 0) return 0;
	int64 r;
	while ((r = y % x) != 0) {
		y = x;
		x = r;
	}
	return x;
}
int64 lcm(int64 x, int64 y) {
	if (x == 0 || y == 0) return 0;
	return x / gcd(x, y) * y;
}

int dx[] = { -1, 0, 1, 0 };
int dy[] = { 0, 1, 0, -1 };

void Main();
signed main() {
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(30);
	Main();
}

/*----------------------------Insert from here!----------------------------*/

/*----------------------------Insert above here----------------------------*/

void Main() {
	int N; cin >> N;
	vector<int> V(N);
	rep(i, N) cin >> V[i];

	auto dp = make_v(N + 1, 2, -INF);
	dp[0][0] = dp[0][1] = 0;
	for (int i = 1; i <= N; ++i) {
		dp[i][0] = max(dp[i - 1][0], dp[i - 1][1]);
		dp[i][1] = dp[i - 1][0] + V[i - 1];
		if (i >= 2) dp[i][1] = max(dp[i][1], dp[i - 2][1] + V[i - 1]);
	}

	cout << max(dp[N][0], dp[N][1]) << endl;
}