#include <fstream>
#include <iostream>

using namespace std;

const int Vmax = 100001;
long long a[Vmax], dp[Vmax];

int main(){
    ifstream fin("oo.in");
    ofstream fout("oo.out");
    int n;
    fin>>n;
    for(int i=1;i<=n;i++)
        fin>>a[i];
    for(int i=1;i<=n-1;i++){
        dp[i] = a[i] + a[i-1] + dp[i-3];
    }
    long long solutie=dp[n-1];
    dp[1]=0;
    dp[2]=0;
    for(int i=3;i<=n;i++){
        dp[i] = max(dp[i-1], a[i] + a[i-1] + dp[i-3]);
    }
    fout<<max(solutie, dp[n]);
}