#include <iostream>
#include <fstream>
using namespace std;
const int dim=1e5+2;
ifstream f("oo.in");
ofstream g("oo.out");
int v[dim],s[dim];
int main()
{
    int n,i,j,mx=0;
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
    }
    s[2]=s[3]=s[4]=v[1]+v[2];
    for(i=1;i<n;i++)
    {
        s[i]=max(s[i-1],v[i]+v[i-1]+s[i-3]);
        if(s[i]>mx)
            mx=s[i];
    }
    g<<mx;
    return 0;
}