#include <bits/stdc++.h>

#define rep(i, n, s) for(int (i) = 0; (i) < (n); (i) += (s))

using namespace std;

int main()
{
  int num, result = 0;
  cin >> num;

  vector<int> v(num + 5, 0);

  for (int i = 0; i < num; i++)
  {
    int tmp;
    cin >> tmp;
    v[i] = tmp;
  }

  for (int i = 0; i < num; i++)
  {
    if ((v[i] + v[i + 2]) > (v[i + 1] + v[i + 3]))
    {
      result += v[i];
      i++;
    }
  }

  cout << result << endl;
}