#include <iostream>
#include <vector>
using namespace std;
template <class T>
inline bool chmax(T &a, T b)
{
  if (a < b)
  {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T &a, T b)
{
  if (a > b)
  {
    a = b;
    return 1;
  }
  return 0;
}

int N;
long long v[10000];

long long dp[10000];

int main()
{
  int N;
  cin >> N;
  for (int i = 0; i < N; ++i)
    cin >> v[i];
  for (int i = 0; i < 10000; ++i)
    dp[i] = 0;

  dp[0] = v[0];
  dp[1] = v[1];
  if (N > 1)
  {
    for (int i = 2; i < N; ++i)
    {
      chmax(dp[i], dp[i - 2] + v[i]);
      if (i > 2)
        chmax(dp[i], dp[i - 3] + v[i]);
    }

    if (dp[N - 1] > dp[N - 2])
    {
      cout << dp[N - 1] << endl;
    }
    else
    {
      cout << dp[N - 2] << endl;
    }
  }
  else
  {
    cout << v[0] << endl;
  }
}