#include <fstream>
#include <iostream>
#include <math.h>
#define NMax 100005
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int N,sp[NMax],dp[NMax],i,sol;
void read()
{
    int y;
    fin>>N;
    for(i=1;i<=N;i++)
    {
        fin>>y;
        sp[i]=y;
    }
}
void solve()
{

    for(i=1;i<=N-1;i++)
    {
        if(i==3 && (dp[i-1]<=(sp[i]+sp[i+1]))){N++;}
        if(i==2 && (dp[i-1]>(sp[i]+sp[i+1])) && (sp[i+2]+sp[i+3]<dp[i-1])){N--;}
        dp[i]=max(dp[i-3]+sp[i]+sp[i+1],dp[i-1]);
        sol=max(sol,dp[i]);
    }
}
void print()
{
    fout<<sol<<"\n";
}
int main()
{
    read();
    solve();
    print();
    return 0;
}