fn read<T: std::str::FromStr>() -> T {
  let mut s = String::new();
  std::io::stdin().read_line(&mut s).ok();
  s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn main() {
  let n: usize = read();
  let ds: Vec<u32> = read_vec();
  println!("{}", no45(n, ds));
}

fn no45(max: usize, ds: Vec<u32>) -> u32 {
  
  fn get_next(start_index: usize, current_index: usize, ds: &[u32]) -> Option<(usize, u32)> {
    let next_index = if start_index == current_index {
      current_index + 2
    } else {
      current_index + 1
    };

    if next_index >= ds.len() {
      None
    } else {
      Some((next_index, ds[next_index]))
    }
  }

  let mut start_index = 0;
  let mut current_index = 0;
  let mut values = ds.clone();
  loop {
    if let Some((next_index, value)) = get_next(start_index, current_index, &ds) {
      if values[start_index] + value > values[next_index] {
        values[next_index] = values[start_index] + value;
      }
      current_index = next_index;
    } else {
      if start_index + 1 >= max {
        break;
      }

      start_index += 1;
      current_index = start_index;
    }
  }

  *values.iter().max().unwrap()
}