#include <fstream>

using namespace std;

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

int n, w[100005], v[100005], maxim1, maxim2, maxim3;

int main()
{
    fin>>n;
    for(int i = 1; i <= n; i++){
        fin>>v[i];
    }
    w[1] = 0;
    w[2] = 0;
    w[3] = v[2] + v[3];
    for(int i = 4; i <= n; i++){
        if(w[i - 1] < v[i] + v[i - 1] + w[i - 3]){
            w[i] =  v[i] + v[i - 1] + w[i - 3];
        }
        else{
            w[i] = w[i - 1];
        }
    }
    maxim1 = w[n];
    w[1] = v[1] + v[n];
    w[2] = max(v[n]+v[1],v[1]+v[2]);
    w[3] = max(w[2], v[3]+v[4]);
    for(int i = 4; i < n; i++){
        if(w[i - 1] < v[i] + v[i - 1] + w[i - 3]){
            w[i] =  v[i] + v[i - 1] + w[i - 3];
        }
        else{
            w[i] = w[i - 1];
        }
    }
    maxim2 = w[n - 2];

    w[1] = 0;
    w[2] = v[1] + v[2];
    w[3] = max(v[1]+v[2],v[2]+v[3]);
    for(int i = 4; i <= n; i++){
        if(w[i - 1] < v[i] + v[i - 1] + w[i - 3]){
            w[i] =  v[i] + v[i - 1] + w[i - 3];
        }
        else{
            w[i] = w[i - 1];
        }
    }
    maxim3 = w[n - 1];
    fout<<max(maxim1, max(maxim2, maxim3));
    return 0;
}