#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <array>
#include <map>
#include <stack>
#include <queue>
#include <set>

using namespace std;

int main() {

    int N;
    cin >> N;

    vector<int> v(N);

    int n;
    for (int i = 0; i < N; ++i) {
        cin >> n;
        v[i] = n;
    }

    vector<int> dp(N + 2);
    dp[0] = 0;
    dp[1] = 0;
    for (int j = 2; j < N + 2; ++j) {
        dp[j] = max(dp[j - 2] + v[j - 2], dp[j - 1]);
    }

    cout << dp[N + 1] << "\n";

    return 0;
}