#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
long long n, v[100001], dp[100001], rez;

int main()
{
    fin>>n;
    for(int i=1; i<=n; i++)
        fin>>v[i];

    ///cazul 1
    dp[1] = v[1];
    dp[2] = v[1]  + v[2];
    dp[3] = v[1] + v[2];
    for(int i=4; i<n; i++)
        dp[i] = max(dp[i-1], v[i] + v[i-1] + dp[i-3]);
    rez=dp[n-1];



    ///cazul 2
    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-1], v[i] + v[i-1] + dp[i-3]);
    rez=max(rez, dp[n-2]);


    ///cazul 3
    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], v[i] + v[i-1] + dp[i-3]);
    rez=max(rez, dp[n]);


    fout<<rez;
    return 0;
}