#include <fstream>

using namespace std;
ifstream fi("oo.in");
ofstream fo("oo.out");
unsigned n;
unsigned s1,s2,s3;
unsigned X[100001],S[100001];

unsigned suma(unsigned a, unsigned b)
{
    for(int i=a; i<=b; i++)
        S[i]=max(S[i-3]+X[i-1]+X[i],S[i-1]);
    return S[b];
}

int main()
{
    fi>>n;
    for(int i=1; i<=n; i++)
        fi>>X[i];
    S[3]=X[2]+X[3];
    s1=suma(4,n);
    S[2]=X[1]+X[2];
    s2=suma(3,n-1);
    S[1]=X[1]+X[n];
    s3=suma(3,n-2);
    fo<<max(s1,max(s2,s3));
    fi.close();
    fo.close();
    return 0;
}