#include <bits/stdc++.h>
using namespace std;

int a[100004], n, dp[100004];
ifstream fin("oo.in");
ofstream fout("oo.out");

int main()
{
    int i, M;
    fin >> n;
    for (i = 1; i <= n; i++)
        fin >> a[i];

    /// aleg obligatoriu pe a[1]+a[2]
    dp[1] = 0;
    dp[2] = a[1] + a[2];
    dp[3] = dp[2];
    dp[4] = dp[3];
    for (i = 5; i < n; i++)
        dp[i] = max(dp[i-1], a[i]+a[i-1]+dp[i-3]);
    M = dp[n - 1];

    /// aleg obligatoriu pe a[2]+a[3]
    dp[1] = 0;
    dp[2] = 0;
    dp[3] = a[2] + a[3];
    dp[4] = dp[5] = dp[3];
    for (i = 6; i <= n; i++)
        dp[i] = max(dp[i-1], a[i]+a[i-1]+dp[i-3]);
    M = max(M, dp[n]);

    /// aleg obligatoriu pe a[1] + a[n]
    dp[1] = a[1] + a[n];
    dp[2] = dp[3] = dp[1];
    for (i = 4; i <= n - 2; i++)
        dp[i] = max(dp[i-1], a[i]+a[i-1]+dp[i-3]);

    M = max(M, dp[n - 2]);

    fout << M << "\n";
    fout.close();
    return 0;
}