#include <iostream>
#include <fstream>
using namespace std;

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

#define nmax 100005
int n, v[nmax], dp[nmax];

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

    // Case 1: don't use sector N in any pair (pairs go up to (N-2, N-1))
    dp[0] = 0; dp[1] = 0; dp[2] = 0;
    for (int i = 3; i <= n; i++)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 2] + v[i - 1]);
    int ans = dp[n];

    // Case 2: don't use sector 1 in any pair (pairs go from (2,3) up to (N-1,N))
    dp[0] = 0; dp[1] = 0; dp[2] = 0;
    for (int i = 3; i <= n + 1; i++)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    ans = max(ans, dp[n + 1]);  // Hmm, indexing gets messy...

    fout << ans;
    return 0;
}