#include<iostream>
#include<fstream>
#include<algorithm>
#include<vector>
#define NMAX 100002
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int a[NMAX],uz[NMAX];
int n;
vector<int>s(NMAX,-1);
void read()
{
    fin>>n;
    for(int i=1;i<=n;i++)
        fin>>a[i];
    fin.close();

}
int solve(int i)
{
    int x1,x2;

    if(s[i]!=-1)
    {if(!uz[i])uz[i]=1; return s[i];}
    x1=solve(i-1);
    x2=solve(i-3)+a[i]+a[i-1];
    if(i==n)
   {
       if(uz[i-1])x1=0;
        if(uz[i-3])x2=0;
   }
    s[i]=max(x1,x2);
    return s[i];
}
int main()
{
    read();
    s[0]=0;s[1]=0;s[2]=a[1]+a[2];
   uz[2]=1;
   fout<<solve(n);

    fout.close();
    return 0;
}