#include <iostream>
#include <algorithm>

using namespace std;

int maxHappiness(int n, int a[]) {
    if (n == 0) return 0;
    if (n == 1) return max(0, a[0]);

    int dp[n + 1];
    dp[0] = 0;
    dp[1] = max(0, a[0]);

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

    return dp[n];
}

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

    cout << maxHappiness(n, a) << endl;

    return 0;
}