#include <bits/stdc++.h>

using namespace std;

const int MAX_N = 100000;

int n, ans = -1;
int dp[MAX_N + 1];
vector <int> v;

int main()
{
    ios_base :: sync_with_stdio(0);
    cin.tie(0);

    freopen("oo.in", "r", stdin);
    freopen("oo.out", "w", stdout);

    cin >> n;
    v.resize(n + 1);
    for(int i = 1; i <= n; i ++)
        cin >> v[i];

    dp[1] = 0;
    dp[2] = v[1] + v[2];
    dp[3] = v[1] + v[2];
    for(int i = 4; i <= n - 1; i ++)
        dp[i] = max(dp[i - 3] + v[i - 1] + v[i], dp[i - 1]);
    ans = max(ans, dp[n - 1]);
//    cout << dp[n - 1] << "\n";

    dp[1] = 0;
    dp[2] = 0;
    dp[3] = v[2] + v[3];
    dp[4] = v[2] + v[3];
    for(int i = 5; i <= n; i ++)
        dp[i] = max(dp[i - 3] + v[i - 1] + v[i], dp[i - 1]);
    ans = max(ans, dp[n]);
//    cout << dp[n] << "\n";

    dp[1] = v[1] + v[n];
    dp[2] = v[1] + v[n];
    for(int i = 3; i <= n - 2 ; i ++)
        dp[i] = max(dp[i - 3] + v[i - 1] + v[i], dp[i - 1]);
    ans = max(ans, dp[n - 2]);
//    cout << dp[n - 2] << "\n";

    cout << ans;
    return 0;
}