#include <iostream>
#include <fstream>


using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int v[100001];
int n;
int rez(int a,int b)
{
    int dp[100003];
    dp[a+1]=v[a+1]+v[a];
    for(int i=a+2;i<=b;i++)
    {
        dp[i]=max(dp[i-1],dp[i-3]+v[i]+v[i-1]);
    }
    return dp[b];
}
int main()
{
    fin>>n;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    fout<<max(rez(1,n-1),max(rez(2,n),rez(3,n+1)));

    return 0;
}