#include <bits/stdc++.h>

using namespace std;

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

int dp[100003], a[100003], n;

/**
dp[i] = suma max obt din primele i numere
a = 3 7 5 -1 6  6  2
dp= 3 7 8 8 14 14 16
dp[i] = max(dp[i - 1], dp[i - 2] + a[i]), 0)
*/

int main()
{
    int M, i;
    fin >> n;
    for(i = 1; i <= n; i++)
        fin >> a[i];
    /// aleg obligatoriu pe a[1] + a[2]
    dp[2] = a[1] + a[2];
    dp[3] = dp[2];
    dp[4] = dp[3];
    for(i = 5; i < n; i++)
        dp[i] = max(dp[i - 1], a[i] + a[i - 1] + dp[i - 3]);
    M = dp[n - 1];
    /// aleg obligatoriu pe a[2] + a[3]
    dp[1] = dp[2] = 0;
    dp[3] = a[2] + a[3];
    dp[4] = dp[5] = dp[3];
    for(i = 6; i <= n; i++)
        dp[i] = max(dp[i - 1], a[i] + a[i - 1] + dp[i - 3]);
    M = max(M, dp[n]);
    ///aleg obligatoriu pe a[n] + a[1]
    dp[1] = a[1] + a[n];
    dp[2] = dp[3] = dp[1];
    for(i = 4; i < n - 1; i++)
        dp[i] = max(dp[i - 1], a[i] + a[i - 1] + dp[i -3]);
    M = max(M, dp[n - 2]);
    fout << M;
    fin.close();
    fout.close();
    return 0;
}