#include <bits/stdc++.h>

using namespace std;


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


int dp[100001], a[100001];

int n;

int main()
{
    in >> n;
    for(int i = 1; i <= n; i++)
        in >> a[i];
    int maxim = 0, poz = 0, sum = 0;
    for(int i = 1; i <= n; i++)
    {
        if(a[i] + a[i + 1] > maxim)
        {
            maxim = a[i] + a[i + 1];
        }
    }
    for(int i = 1; i <= n; i++)
    {
        if(a[i] + a[i + 1] == maxim)
            poz = i;
    }
    for(int i = poz; i >= 1; i -= 4)
    {
       sum += a[i];
       sum += a[i + 1];
    }
    for(int i = poz; i <= n; i += 4)
    {
        if(i != poz)
        {
            sum += a[i];
            sum += a[i - 1];
        }
    }
    out << sum;
    return 0;
}