#define _GLIBCXX_DEBUG 0
#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
#include <unordered_map>
#include "optimization.h"
#include <map>

#define all(a) a.begin, a.end()
using namespace std;
int main() {
    int n;
    cin >> n;
    vector<int> value(n+1);
    vector<int> dp(n+1);
    for (int i = 1; i <= n; i++){
        cin >> value[i];
    }
    dp[1] = value[1];
    for (int i = 2; i <= n; i++){
        dp[i] = max(dp[i-1], dp[i-2]) + value[i];
    }
    cout << dp[n];
}