#include <bits/stdc++.h>
using namespace std;
ifstream f("oo.in");
ofstream g("oo.out");

const int nmax=100005;
int dinamica[nmax],val[nmax];
int i,n;

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

    for (i=2;i<n;i++)
       dinamica[i]=max(val[i]+val[i-1]+dinamica[i-3],dinamica[i-1]);

    g<<dinamica[n-1];
    return 0;
}