#include <bits/stdc++.h>
using namespace std;

int main() {
    int N, V[1010] = {};
    cin >> N;
    for (int i = 0; i < N; i++) {
        cin >> V[i + 2];
    }

    int dp[1010] = {};
    for (int i = 0; i < N + 2; i++) {
        dp[i + 1] = max(dp[i + 1], dp[i]);
        dp[i + 2] = max(dp[i + 2], dp[i] + V[i + 2]);
    }
    cout << dp[N + 1] << endl;
}