#include <fstream>
#include <string.h>
#define nMax 100001
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int dp[nMax], v[nMax], n, maximum;
int solve1()
{
    int maxim=0;
    memset(dp, 0, sizeof(dp));
    for(int i=3;i<=n;i++)
    {
        maxim=max(maxim, dp[i-3]);
        dp[i]=maxim+v[i]+v[i-1];
        maximum=max(maximum, dp[i]);
    }
    return maxim;
}
int solve2()
{
    int maxim=0;
    memset(dp, 0, sizeof(dp));
    for(int i=2;i<n;i++)
    {
        if(i>=3)
            maxim=max(maxim, dp[i-3]);
        dp[i]=maxim+v[i]+v[i-1];
        maximum=max(maximum, dp[i]);
    }
    return maxim;
}
int solve3()
{
    int maxim=0;
    memset(dp, 0, sizeof(dp));
    dp[1]=v[1]+v[n];
    for(int i=4;i<n-1;i++)
    {
        maxim=max(maxim, dp[i-3]);
        dp[i]=maxim+v[i]+v[i-1];
        maximum=max(maximum, dp[i]);
    }
    return maxim;
}
void read()
{
    fin>>n;
    for(int i=1;i<=n;i++)
        fin>>v[i];
}
void write()
{
    fout<<maximum;
}
int main()
{
    read();
    solve1();
    solve2();
    solve3();
    write();
    return 0;
}