#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <math.h>
#include <set>
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define P pair<int, int>

#define MOD 1000000007
#define INF 1012345678
#define NINF (-2147483647-1)
#define LLINF 9223372036854775807
using ll = long long;
using namespace std;

int N;

int f(int p, vector<int> V) {
    if (p < N) {
        return max(f(p + 1, V), f(p + 2, V) + V[p]);
    }
    else {
        return 0;
    }
}

int main() {
    cin >> N;
    vector<int> V(N);
    for (int i = 0; i < N; i++)
    {
        cin >> V[i];
    }
    cout << f(0, V) << endl;
    getchar(); getchar();
    return 0;
}