#include <bits/stdc++.h>

#define Nmax 100002

using namespace std;

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

int N;
int A[Nmax];
int S;
int i;
int dp[Nmax];
int sol;

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