#include <fstream>
#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 x,y;
    fin>>N;
    fin>>x;
    for(i=2;i<=N;i++)
    {
        fin>>y;
        sp[i-1]=x+y;
        x=y;
    }
}
void solve()
{
    dp[1]=sp[1];
    dp[2]=max(sp[2],dp[1]);
    dp[3]=max(sp[3],dp[2]);
    sol=max(sp[1],max(sp[2],sp[3]));
    N=N-1-(N%2);
    for(i=4;i<=N;i++)
    {
        dp[i]=max(dp[i-3]+sp[i],max(dp[i-2],dp[i-1]));
        sol=max(sol,dp[i]);
    }
}
void print()
{
    fout<<sol<<"\n";
}
int main()
{
    read();
    solve();
    print();
    return 0;
}