#include <bits/stdc++.h>
#define DIM 100005

using namespace std;

ifstream f("oo.in");
ofstream g("oo.out");

int n, m, v[DIM], dp[DIM], sol;

int main()
{
    f >> n;
    for(int i = 1; i <= n; i++)
        f >> v[i];

    dp[1] = v[1];
    dp[2] = v[1] + v[2];
    dp[3] = v[1] + v[2];

    for(int i = 4; i < n; i++)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);

    sol = dp[n - 1];

    for(int i = 1; i <= n; i++)
        dp[i] = 0;

    dp[1] = 0;
    dp[2] = v[2];
    dp[3] = v[2] + v[3];

    for(int i = 4; i <= n; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);

    sol = max(sol, dp[n]);

    for(int i = 1; i <= n; i++)
        dp[i] = 0;

    dp[1] = v[1] + v[n];
    dp[2] = v[1] + v[n];
    dp[3] = v[1] + v[n];

    for(int i = 4; i < n - 1; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);

    sol = max(sol, dp[n - 2]);

    g << sol;
    return 0;
}