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

template <class T> bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    } else {
        return false;
    }
}

int main() {
    int N;
    cin >> N;
    vector<int> V(N);
    for (int i = 0; i < N; ++i) cin >> V[i];

    vector<int> dp(N + 1, -1);
    dp[0] = 0;
    dp[1] = V[0];
    for (int i = 2; i <= N; ++i) {
        chmax(dp[i], dp[i - 2] + V[i - 1]);
        chmax(dp[i], dp[i - 1]);
    }

    cout << dp[N] << endl;
}