#include <algorithm>
#include <numeric>
#include <string>
#include <vector>
#include <iostream>
#include <queue>
#include <utility>
#include <cmath>
#include <map>
#include <unordered_map>
#include <functional>
#include <fstream>
using namespace std;

using ull = unsigned long long;

int main()
{
    int dp[1001];
    int n;
    cin >> n;
    vector<int> V(n);

    for(auto&& x : V)
    {
        cin >> x;
    }

    if(n == 1)
    {
        cout << V.at(0) << endl;
        return 0;
    }

    dp[0] = V.at(0);
    dp[1] = max(dp[0],V.at(1));

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

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