#include <bits/stdc++.h>

using namespace std;
ifstream f("oo.in");
ofstream g("oo.out");
deque <pair <int,int>> deq;
int n,i,v[100005],din[100005],maxim;
int main()
{
    f>>n;
    for (i=1;i<=n;i++)
    {
        f>>v[i];
    }
    for (i=n+1;i<=n;i++)
    {
        v[i]=v[n-i];
    }
    deq.push_back({0,0});
    for (i=3;i<=2*n;i++)
    {
        while (!deq.empty()&&deq.front().first-1<i-n+1)
        {
            deq.pop_front();
        }
        din[i]=deq.front().second+v[i]+v[i-1];
        if (din[i]>maxim)
        {
            maxim=din[i];
        }
        while (!deq.empty()&&deq.back().second<din[i-2])
        {
            deq.pop_back();
        }
        deq.push_back({i-2,din[i-2]});
    }
    g<<maxim;
    return 0;
}