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

using namespace std;

int main() {
    int n;
    cin >> n; // number of plates

    vector<int> v(n);
    for (int i = 0; i < n; ++i) {
        cin >> v[i]; // deliciousness of each plate
    }

    if (n == 0) {
        cout << 0 << "\n";
        return 0;
    }
    if (n == 1) {
        cout << v[0] << "\n";
        return 0;
    }

    // Dynamic programming
    vector<int> dp(n);
    dp[0] = v[0];
    dp[1] = max(v[0], v[1]);

    for (int i = 2; i < n; ++i) {
        dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
    }

    cout << dp[n - 1] <<endl; // final answer
    return 0;
}