#include <iostream>
#include <unordered_map>
using namespace std;
int n;
int v[1000];
int memo[1000][505] = {0};
int solve(int i, int d)
{
    if(i >= n)
        return 0;
    if(memo[i][d] > 0)
        return memo[i][d];
    return memo[i][d] = max(solve(i + 2, d + 1), solve(i + 3, d + 1)) + v[i];
}
int main(void)
{
    cin >> n;
    for(int i = 0; i < n; i++)
        cin >> v[i];
    cout << max(solve(2, 0), max(solve(0, 0), solve(1, 0))) << endl;
    return 0;
}