#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>
#include <climits>
#include <unordered_map>
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");

const int LMAX = 100005;
int dp[LMAX], v[LMAX];

int main() {
    int n, i, m1;
    fin>>n;
    fin>>v[1]>>v[2];
    dp[2] = v[2] + v[1];
    for (i = 3; i < n; i++) {
        fin>>v[i];
        dp[i] = max(dp[i-1], v[i-1] + v[i] + dp[i-3]);
    }
    m1 = dp[n-1];
    dp[1] = dp[2] = 0;
    for(i = 3; i <= n; i++) {
        dp[i] = max(dp[i-1], v[i-1] + v[i] + dp[i-3]);
    }
    fout<<max(m1, dp[n]);


    fin.close();
    fout.close();
    return 0;
}