#include <bits/stdc++.h>

using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int n, v[100001], ans[100001], rez;
int solve(int ls, int ld)
{
    ans[ls] = ans[ls - 1] = 0;
    ans[ls + 1] = v[ls] + v[ls + 1];
    for(int i = ls + 2; i <= ld; ++ i)
        ans[i] = max(ans[i - 1], ans[i - 3] + v[i] + v[i - 1]);
    return ans[ld];
}
int main()
{
    fin >> n;
    for(int i = 1; i <= n; ++ i)
        fin >> v[i];
    rez = solve(1, n -1);
    rez = max(rez, solve(2, n));
    rez = max(rez, solve(3, n - 2));
    fout << rez;
    return 0;
}