#include <iostream>
using namespace std;
int v[100000],d[100000],n;
int din(int plussy)
{
    for(int i=1+plussy;i<n+plussy-1;i++)
    {
        if(i<2)
            d[i] = max(d[i - 1], d[0] + v[i - 1] + v[i]);
        else
            d[i] = max(d[i - 1], d[i - 3] + v[i - 1] + v[i]);
    }
    return d[plussy + n - 2];
}
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>v[i];
    }
    int maxi = max(din(0),max(din(1),din(2)));
    cout<<maxi;
    return 0;
}