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

ifstream fin("oo.in");
ofstream fout("oo.out");

int n, a[100001], dp[100001], i, j, k;

int p(int i, int j){
    dp[i] = 0;
    dp[i+1] = a[i] + a[i+1];
    for(k=i+2;k<=j;k++){
        dp[k] = max((a[k] + a[k-1] + dp[k-3]), dp[k-1]);
    }
    return dp[j];
}

int main()
{
    fin>>n;
    for(i=1;i<=n;i++){
        fin>>a[i];
    }

    fout<<max(p(1, n-1), max(p(2, n),p(3, n+1)));
    return 0;
}