#include <bits/stdc++.h>

using namespace std;

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


int n , dp1[100005], a[100005], dp2[100005];


/**


1 2 3 4 5


dp[i - 3] + a[i - 1] + a[i] , dp[i - 1]
*/

int main()
{
    fin >> n;
    for (int i = 1; i <= n; i++)
        fin >> a[i];
    dp1[1] = a[1] + a[2];
    dp1[2] = dp1[1];
    for (int i = 3; i < n - 1; i++)
        dp1[i] = max (dp1[i - 1], dp1[i - 3] + a[i] + a[i + 1]);
    dp2[1] = 0;
    dp2[2] = a[2] + a[3];
    for (int i = 3; i < n; i++)
        dp2[i] = max (dp2[i - 1], dp2[i - 3] + a[i] + a[i + 1]);
    int maxim = 0;
    for (int i = 1; i <= n; i++)
        maxim = max ({dp1[i], dp2[i], maxim});
    fout << maxim << "\n";
    return 0;
}