#include <algorithm>
#include <fstream>
#include <vector>
using namespace std;

ifstream cin("oo.in");
ofstream cout("oo.out");

int v[100005], dp[100005];
int contor, dim, ok;
int n, i, j, l;

int main()
{
    cin >> n;
    for(int i = 1; i <= n; i++)
        cin >> v[i];
    
    dp[1] = v[1] + v[n];
    dp[2] = dp[1];
    dp[3] = dp[2];
    for(int i = 4; i < n - 1; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);
    contor = max(contor, dp[n - 2]);

    dp[1] = v[1] + v[2];
    dp[2] = v[1] + v[2];
    dp[3] = dp[2];
    dp[4] = dp[3];
    for(int i = 5; i < n; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);
    contor = max(contor, dp[n - 1]);

    dp[1] = 0;
    dp[2] = 0;
    dp[3] = v[3] + v[2];
    dp[4] = dp[3];
    dp[5] = dp[3];
    for(int i = 6; i <= n; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);
    contor = max(contor, dp[n]);

    cout << contor << '\n';
    return 0;
}