#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

#define MOD 1000000007
#define MOD2 998244353
#define int long long
#define double long double
#define EPS 1e-9
//#define PI 3.14159265358979

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

using namespace std;

template < typename T >
ostream &operator<<(ostream &os, const vector< T > &A) {
	for (int i = 0; i < A.size(); i++)
		os << A[i] << " ";
	os << endl;
	return os;
}
template <>
ostream &operator<<(ostream &os, const vector< vector< int > > &A) {
	int N = A.size();
	int M;
	if (N > 0)
		M = A[0].size();
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < M; j++)
			os << A[i][j] << " ";
		os << endl;
	}
	return os;
}

typedef pair< int, int > pii;
typedef long long ll;

struct edge {
	int from, to, d, c;
	edge(int _from = 0, int _to = 0, int _d = 0, int _c = 0) {
		from = _from;
		to = _to;
		d = _d;
		c = _c;
	}
	bool operator<(const edge &rhs) const {
		return (d == rhs.d) ? (c < rhs.c) : (d < rhs.d);
	}
};
struct aabb {
	int x1, y1, x2, y2;
	aabb(int x1, int y1, int x2, int y2) : x1(x1), y1(y1), x2(x2), y2(y2) {}
};

typedef vector< edge > edges;
typedef vector< edges > graph;
struct flow {
	int to, cap, rev, cost;
	flow(int to = 0, int cap = 0, int rev = 0, int cost = 0) : to(to), cap(cap), rev(rev), cost(cost) {}
};
typedef vector< vector< flow > > flows;

const int di[4] = {0, -1, 0, 1};
const int dj[4] = {-1, 0, 1, 0};
const int ci[5] = {0, 0, -1, 0, 1};
const int cj[5] = {0, -1, 0, 1, 0};
const ll LINF = LLONG_MAX / 2;
const int INF = INT_MAX / 2;
const double PI = acos(-1);

int pow2(int n) { return 1LL << n; }
template < typename T, typename U >
bool chmin(T &x, const U &y) {
	if (x > y) {
		x = y;
		return true;
	}
	return false;
}
template < typename T, typename U >
bool chmax(T &x, const U &y) {
	if (x < y) {
		x = y;
		return true;
	}
	return false;
}

struct initializer {
	initializer() {
		cout << fixed << setprecision(20);
	}
};
initializer _____;

int N, M, K, T, Q, H, W;
int dfs(vector< int > &A, int l, int r, int k) {
	if (k <= 0)
		return 0;
	if (r < l)
		return -LINF;
	int M = r - l + 1;
	if (M % 2 == 0) {
		if (M / 2 < k)
			return -LINF;
		int ret = -LINF;
		int s = 0;
		for (int i = l; i <= r; i += 2)
			s += A[i];
		chmax(ret, s);
		for (int j = r - 1; j >= l; j -= 2) {
			s -= A[j];
			s += A[j + 1];
			chmax(ret, s);
		}
		//cout << l << " " << r << " " << k << " " << ret << endl;
		return ret;
	} else {
		int ret = -LINF;
		if (k & 1) {
			chmax(ret, dfs(A, l, l + M / 2 - 2, k / 2) + dfs(A, l + M / 2 + 2, r, k / 2) + A[l + M / 2]);
			chmax(ret, dfs(A, l, l + M / 2 - 1, k / 2 + 1) + dfs(A, l + M / 2 + 1, r, k / 2));
			chmax(ret, dfs(A, l, l + M / 2 - 1, k / 2) + dfs(A, l + M / 2 + 1, r, k / 2 + 1));
		} else {
			chmax(ret, dfs(A, l, l + M / 2 - 1, k / 2) + dfs(A, l + M / 2 + 1, r, k / 2));
			chmax(ret, dfs(A, l, l + M / 2 - 2, k / 2 - 1) + dfs(A, l + M / 2 + 2, r, k / 2) + A[l + M / 2]);
			chmax(ret, dfs(A, l, l + M / 2 - 2, k / 2) + dfs(A, l + M / 2 + 2, r, k / 2 - 1) + A[l + M / 2]);
		}
		//cout << l << " " << r << " " << k << " " << ret << endl;
		return ret;
	}
	return 0;
}
signed main() {
	cin >> N;
	vector< int > A(N);
	rep(i, N) cin >> A[i];
	cout << dfs(A, 0, N - 1, N / 2) << endl;
	//cout << dfs(A, 0, 4, 2);
	return 0;
}

Measured memory_bytes: 4828