public static int pageCount(int n, int p)
    {
      if (n % 2 == 1) n--;
      int l2R = 0, r2L = 0;
      for (int i = 1; i < p; i += 2) l2R++;
      for (int i = n; i > p; i -= 2) r2L++;
      return Math.Min(l2R, r2L);
    }