#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(){
    int n;
    cin >> n;
    vector<int> v(n);
    for(int i=0; i<n; ++i){
        cin >> v[i];
    }
    vector<vector<int>> cache(n+3, vector<int>(2, 0));
    for(int i=n-1; i>=0; --i){
        cache[i][false]=max(
                max(cache[i+1][false], cache[i+1][true]),
                max(cache[i+2][false], cache[i+2][true]));
        cache[i][true]=max(
                max(cache[i+2][false], cache[i+2][true]),
                max(cache[i+3][false], cache[i+3][true]))+v[i];
    }
    cout << max(cache[0][true], cache[0][false]) << endl;
    return 0;
}