#include <bits/stdc++.h>
using namespace std;

int n,A[100010],DP[100010],ans;

int main(){
    freopen("oo.in","r",stdin);
    freopen("oo.out","w",stdout);
    cin>>n;
    for (int i=1; i<=n; i++) cin>>A[i];
    A[0]=A[n];
    DP[1]=A[0]+A[1];
    DP[2]=max(DP[1],A[1]+A[2]);
    DP[3]=max(DP[2],A[2]+A[3]);
    for (int i=4; i<=n; i++){
        DP[i]=max(DP[i-1],DP[i-4]+A[i]+A[i-1]);
    }
    //for (int i=1; i<=n; i++) cout<<DP[i]<<" ";
    cout<<DP[n];
    return 0;
}