#include<bits/stdc++.h>
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
long long n, v[100005], dp[100005];
int main(){
    fin >> n;
    for(int i = 1; i <= n; i++)
        fin >> v[i];
    long long max1 = 0;
    dp[1] = v[1] + v[n];
    dp[2] = dp[1];
    dp[3] = dp[2];
    for(int i = 4; i < n - 1; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);
    max1 = max(dp[n - 2],max1);
    dp[1] = v[1] + v[2];
    dp[2] = v[1] + v[2];
    dp[3] = dp[2];
    dp[4] = dp[3];
    for(int i = 5; i < n; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);
    max1 = max(dp[n - 1], max1);
    dp[1] = 0;
    dp[2] = 0;
    dp[3] = v[3] + v[2];
    dp[4] = dp[3];
    dp[5] = dp[3];
    for(int i = 6; i <= n; i++)
        dp[i] = max(dp[i - 3] + v[i] + v[i - 1], dp[i - 1]);
    fout << max(dp[n], max1);
    return 0;
}