#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("oo");
ofstream fout("oo.out");

const int dim = 1e5+2;
int v[dim], s[dim];

int main()
{
    int i, j, n, rez = 0;
    fin>>n;
    for(i = 1; i < n; i++){
        fin>>v[i];
    }

    s[2] = s[3] = s[4] = v[1] + v[2];
    for(i = 5; i < n; i++){
        s[i] = max(s[i-1], v[i-1] + v[i] + s[i-3]);
    }
    rez = s[n-1];

    s[1] = s[2] = s[3] = v[1] + v[n];
    for(i = 4; i < n-1; i++){
        s[i] = max(s[i-1], v[i-1] + v[i] + s[i-3]);
    }
    rez = max(rez, s[n-2]);

    s[1] = s[2] = 0;
    for(i = 3; i <= n; i++){
        s[i] = max(s[i-1], v[i-1] + v[i] + s[i-3]);
    }
    rez = max(rez, s[n]);

    fout<<rez;
    return 0;
}