#include <fstream>

using namespace std;

const int Nmax = 100005;

long long v[Nmax], dp[Nmax];

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

    int n;
    long long sol;

    fin >> n;

    for(int i = 1; i <= n; i++){
        fin >> v[i];
    }
    sol = 0;

    ///cazul 1
    dp[2] = 0;
    dp[3] = 0;
    dp[4] = v[4] + v[3];
    dp[5] = dp[4];
    dp[6] = dp[4];
    for(int i = 7; i <= n - 2; i++){
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    }
    sol = max(sol, dp[n - 2]);

    ///cazul 2
    dp[0] = 0;
    dp[1] = 0;
    dp[2] = v[1] + v[2];
    dp[3] = dp[2];
    dp[4] = dp[2];
    for(int i = 5; i <= n - 1; i++){
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    }
    sol = max(sol, dp[n - 1]);

    ///cazul 3
    dp[1] = 0;
    dp[2] = 0;
    dp[3] = v[2] + v[3];
    dp[4] = dp[3];
    dp[5] = dp[3];
    for(int i = 6; i <= n; i++){
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    }
    sol = max(sol, dp[n]);

    fout << sol;

    return 0;
}