#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;

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

    int dp[1001] = {};
    dp[0] = vt[0];
    dp[1] = max(vt[0], vt[1]);
    for (int i = 2; i < n; ++i) {
        dp[i] = max(dp[i - 1], dp[i - 2] + vt[i]);
    }

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