#include <bits/stdc++.h>

using namespace std;

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

int dp[100001], a[100001];

int n, M;

int main()
{
    int i, M;
    in >> n;
    for (i = 1; i <= n; i++)
        in >> a[i];
    dp[1] = 0;
    dp[2] = a[1] + a[2];
    dp[3] = dp[4] = dp[2];
    for (i = 5; i < n; i++)
        dp[i] = max(dp[i - 1], a[i] + a[i - 1] + dp[i - 3]);
    M = dp[n - 1];
    dp[1] = dp[2] = 0;
    dp[5] = dp[4] = dp[3] = a[2] + a[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]);
    dp[1] = a[n] + a[1];
    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]);
    out << M;
    return 0;
}