#include <bits/stdc++.h>

using namespace std;

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

int dp1[100001], a[100001], dp2[100001], dp3[100001];

int n;

int main()
{
    in >> n;
    for(int i = 1; i <= n; i++)
        in >> a[i];
    dp1[1] = 0;
    dp1[2] = a[1] + a[2];
    dp1[3] = dp1[4] = dp1[2];
    for(int i = 5; i < n; i++)
    {
        dp1[i] = max(dp1[i - 1], a[i] + a[i - 1] + dp1[i - 3]);
    }
    dp2[1] = dp2[2] = 0;
    dp2[5] = dp2[4] = dp2[2] = a[2] + a[3];
    for(int i = 6; i <= n; i++)
        dp2[i] = max(dp2[i - 1], a[i] + a[i - 1] + dp2[i - 3]);
    dp3[1] = a[n] + a[1];
    dp3[2] = dp3[3] = dp3[1]
    for(int i = 4; i <= n - 2; i++)
        dp3[i] = max(dp3[i - 1], a[i] + a[i - 1] + dp3[i - 3]);
    out << max({dp1[n], dp2[n], dp3[n]});
    return 0;
}