// problema oo

#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>
#include <string>
#include <cstring>
#include <vector>
#include <stack>
#include <queue>
#include <deque>

#define NMax 100000

using namespace std;

ifstream fin("oo.in");
ofstream fout("oo.out");

int n, o[NMax + 3], dp[4][NMax + 3];

void input() {
    fin >> n;
    for (int i = 1; i <= n; ++i) fin >> o[i];
}

void init() {
    dp[0][2] = o[1] + o[2];
    dp[1][3] = o[2] + o[3];
    dp[2][4] = o[3] + o[4];
    dp[3][5] = o[4] + o[5];
    for (int k = 0; k <= 3; ++k)
        for (int i = k + 3; i <= n - (k == 0); ++i)
            dp[k][i] = max(dp[k][i - 1], (dp[k][i - 3] + o[i] + o[i - 1]));
}

void solve() {
    fout << max(dp[0][n - 1], max(dp[1][n], max(dp[2][n], dp[3][n])));
}

int main() {
    input();
    init();
    solve();
}