#include <fstream>
#include <iostream>
using namespace std;

#define nmax 100002

int v[nmax], dp[nmax];
int main()
{
    int i, n;
    ifstream f("oo.in");
    ofstream g("oo.out");
    f >> n;
    for (i = 1; i <= n; ++i)
        f >> v[i];
    dp[1] = v[1] + v[n];
    int sol = 0;

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

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


    g << sol;


    return 0;
}