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

ifstream fin("oo.in");
ofstream fout("oo.out");
int n ;
int dp[100004];
int a[100004];
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];
    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]);
    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;
    fin.close();
    fout.close();
    return 0;
}