#include <iostream>
#include <fstream>

using namespace std;

ifstream f("oo.in");
ofstream g("oo.out");

int n, ans = -1;
int v[100100], dp[100100];

int main()
{
    f >> n;

    for(int i = 1; i <= n; i++)
        f >> v[i];

    dp[1] = v[1];
    dp[2] = v[2] + v[1];
    dp[4] = dp[3] = dp[2];

    int i;

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

    ans = max(ans, dp[i - 1]);

    dp[1] = v[1];
    dp[3] = dp[2] = dp[1];

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

    ans = max(ans, dp[i - 1] + v[n]);

    dp[1] = 0;

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

    ans = max(ans, dp[i - 1] + v[n - 1] + v[n]);

    g << ans << '\n';

    return 0;
}