#include <iostream>
#include <fstream>

using namespace std;

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

const int maxN = 100005;
int dp[maxN], v[maxN];
int n, ans;

int main()
{
    fin >> n;
    for(int i = 1; i <= n; i++)
        fin >> v[i];
    dp[1] = v[1];
    dp[2] = v[1] + v[2];
    for(int i = 3; i < n; i++)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i] + v[i - 1]);
    ans = dp[n - 1];
    dp[1] = v[1] + v[n];
    dp[2] = v[1] + v[n];
    for(int i = 3; i < n - 1; i++)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i] + v[i - 1]);
    ans = max(ans, dp[n - 2]);
    dp[1] = 0;
    dp[2] = v[2];
    dp[3] = v[2] + v[3];
    for(int i = 4; i <= n; i++)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[1] + v[i - 1]);
    ans = max(ans, dp[n]);
    fout << ans;
    return 0;
}