#include <fstream>
using namespace std;

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

#define NMAX 100005

int v[NMAX];
int dp[NMAX];

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

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

    int maxim = dp[n - 1];

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

    maxim = max(maxim, dp[n]);

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

    fout << maxim;
    return 0;
}